somehow removes search engines:

[ChromiumOS-Guy]

it blocks searchService

/opt/click.ubuntu.com/uwolf.chromiumos-guy/0.6.10/bin/browser/defaults/preferences/custom-prefs.js:99: prefs parse error: unexpected character
[Parent 213689, Main Thread] WARNING: libmaliit-glib.so.0: cannot open shared object file: No such file or directory: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.578: libmaliit-glib.so.0: cannot open shared object file: No such file or directory
[Parent 213689, Main Thread] WARNING: Loading IM context type 'Maliit' failed: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.578: Loading IM context type 'Maliit' failed
[Parent 213689, Main Thread] WARNING: libmaliit-glib.so.0: cannot open shared object file: No such file or directory: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.591: libmaliit-glib.so.0: cannot open shared object file: No such file or directory
[Parent 213689, Main Thread] WARNING: Loading IM context type 'Maliit' failed: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.591: Loading IM context type 'Maliit' failed
[Parent 213689, Main Thread] WARNING: libmaliit-glib.so.0: cannot open shared object file: No such file or directory: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.908: libmaliit-glib.so.0: cannot open shared object file: No such file or directory
[Parent 213689, Main Thread] WARNING: Loading IM context type 'Maliit' failed: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.908: Loading IM context type 'Maliit' failed
[Parent 213689, Main Thread] WARNING: libmaliit-glib.so.0: cannot open shared object file: No such file or directory: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.915: libmaliit-glib.so.0: cannot open shared object file: No such file or directory
[Parent 213689, Main Thread] WARNING: Loading IM context type 'Maliit' failed: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:48.915: Loading IM context type 'Maliit' failed
console.warn: "Browser is executing custom scripts via autoconfig"
console.log: "[OSK Manager]" "OSK Manager Script: Initializing."
console.log: "[OSK Manager]" "OSK Manager Script: Initialization complete. Waiting for commands."
[Parent 213689, Main Thread] WARNING: libmaliit-glib.so.0: cannot open shared object file: No such file or directory: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:49.332: libmaliit-glib.so.0: cannot open shared object file: No such file or directory
[Parent 213689, Main Thread] WARNING: Loading IM context type 'Maliit' failed: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:49.333: Loading IM context type 'Maliit' failed
[Parent 213689, Main Thread] WARNING: libmaliit-glib.so.0: cannot open shared object file: No such file or directory: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:49.334: libmaliit-glib.so.0: cannot open shared object file: No such file or directory
[Parent 213689, Main Thread] WARNING: Loading IM context type 'Maliit' failed: 'glib warning', file /root/.local/share/bsys6/work/librewolf-139.0.4-1/toolkit/xre/nsSigHandlers.cpp:201

(librewolf:213689): Gtk-WARNING **: 16:32:49.334: Loading IM context type 'Maliit' failed
console.log: "[OSK Manager]" "Character count has changed. Showing OSK."
console.log: "[OSK Manager]" "OSK overlay state changed to:" "SHOW"
console.warn: "Access attempt to RS collection \"main/moz-essential-domain-fallbacks\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/remote-permissions\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/url-parser-default-unknown-schemes-interventions\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/anti-tracking-url-decoration\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/query-stripping\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/fingerprinting-protection-overrides\" from local dump was blocked/filtered."
console.log: "[OSK Config Trigger]" "OSK Config Trigger Script: Initializing."
console.log: "[OSK Config Trigger]" "OSK Config Trigger Script: Will dispatch 'OSK_READ_CONFIG_COMMAND' every 200ms. Also listening for clicks outside inputs and URL changes, and URL bar specific events."
console.log: "[OSK Manager]" "New browser window detected:" "chrome://browser/content/browser.xhtml"
console.log: "[OSK Config Trigger]" "DOMContentLoaded event. Sending HIDE command."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_HIDE_COMMAND' command to OSK Manager."
console.log: "[OSK Config Trigger]" "URL bar element found. Setting up listeners."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_READ_CONFIG_COMMAND' command to OSK Manager."
[213689] Sandbox: Couldn't open video device /dev/video
[213689] Sandbox: Couldn't open video device /dev/video2
[213689] Sandbox: Couldn't open video device /dev/video1
console.error: Region.sys.mjs: "Error fetching region" (new TypeError("NetworkError when attempting to fetch resource.", ""))
console.error: Region.sys.mjs: "Failed to fetch region" (new Error("NO_RESULT", "resource://gre/modules/Region.sys.mjs", 372))
console.log: "[OSK Config Trigger]" "DOMContentLoaded event. Sending HIDE command."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_HIDE_COMMAND' command to OSK Manager."
console.log: "[OSK Config Trigger]" "URL bar element found. Setting up listeners."
console.log: "[OSK Config Trigger]" "Pageshow event. Sending HIDE command."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_HIDE_COMMAND' command to OSK Manager."
console.log: "[OSK Config Trigger]" "Load event. Sending HIDE command."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_HIDE_COMMAND' command to OSK Manager."
console.log: "[OSK Config Trigger]" "Pageshow event. Sending HIDE command."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_HIDE_COMMAND' command to OSK Manager."
console.log: "[OSK Manager]" "OSK Manager: Message listener added for window:" "chrome://browser/content/browser.xhtml"
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_HIDE_COMMAND"})
console.log: "[OSK Manager]" "Explicit HIDE command received from trigger. Hiding OSK."
console.log: "[OSK Manager]" "OSK overlay state changed to:" "HIDE"
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_READ_CONFIG_COMMAND"})
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_HIDE_COMMAND"})
console.log: "[OSK Manager]" "Explicit HIDE command received from trigger. Hiding OSK."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_HIDE_COMMAND"})
console.log: "[OSK Manager]" "Explicit HIDE command received from trigger. Hiding OSK."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_READ_CONFIG_COMMAND' command to OSK Manager."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_HIDE_COMMAND"})
console.log: "[OSK Manager]" "Explicit HIDE command received from trigger. Hiding OSK."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_HIDE_COMMAND"})
console.log: "[OSK Manager]" "Explicit HIDE command received from trigger. Hiding OSK."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_READ_CONFIG_COMMAND"})
console.warn: "Access attempt to RS collection \"main/third-party-cookie-blocking-exempt-urls\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/url-classifier-exceptions\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/hijack-blocklists\" from local dump was blocked/filtered."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_READ_CONFIG_COMMAND' command to OSK Manager."
console.warn: "Access attempt to RS collection \"main/search-telemetry-v2\" from local dump was blocked/filtered."
JavaScript error: resource://newtab/lib/TelemetryFeed.sys.mjs, line 1578: Error: Failed to load chrome://pocket/content/pktApi.sys.mjs
console.warn: "Access attempt to RS collection \"main/search-config-v2\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/search-config-overrides-v2\" from local dump was blocked/filtered."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_READ_CONFIG_COMMAND"})
console.warn: "Access attempt to RS collection \"main/newtab-wallpapers-v2\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/top-sites\" from local dump was blocked/filtered."
console.error: SearchEngineSelector: "Received empty search configuration!"
console.log: "[OSK Manager]" "Character count is the same. OSK state unchanged by file read."
console.error: "Received empty top sites configuration!"
console.log: "[OSK Manager]" "Character count is the same. OSK state unchanged by file read."
console.log: "[OSK Manager]" "Character count is the same. OSK state unchanged by file read."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_READ_CONFIG_COMMAND' command to OSK Manager."
console.warn: "Access attempt to RS collection \"main/search-config-v2\" from local dump was blocked/filtered."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_READ_CONFIG_COMMAND"})
console.warn: "Access attempt to RS collection \"main/top-sites\" from local dump was blocked/filtered."
console.error: SearchEngineSelector: "Received empty search configuration!"
console.error: SearchService: "#init: failure initializing search:" [Exception... "Failed to get engine data from Remote Settings"  nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)"  location: "JS frame :: resource://gre/modules/SearchEngineSelector.sys.mjs :: getEngineConfiguration :: line 100"  data: no]
console.error: "Received empty top sites configuration!"
JavaScript error: resource://gre/modules/SearchEngineSelector.sys.mjs, line 100: NS_ERROR_UNEXPECTED: Failed to get engine data from Remote Settings
JavaScript error: resource://gre/modules/SearchEngineSelector.sys.mjs, line 100: NS_ERROR_UNEXPECTED: Failed to get engine data from Remote Settings
JavaScript error: resource://gre/modules/SearchEngineSelector.sys.mjs, line 100: NS_ERROR_UNEXPECTED: Failed to get engine data from Remote Settings
JavaScript error: resource://gre/modules/SearchEngineSelector.sys.mjs, line 100: NS_ERROR_UNEXPECTED: Failed to get engine data from Remote Settings
JavaScript error: resource://gre/modules/SearchEngineSelector.sys.mjs, line 100: NS_ERROR_UNEXPECTED: Failed to get engine data from Remote Settings
JavaScript error: resource://gre/modules/SearchEngineSelector.sys.mjs, line 100: NS_ERROR_UNEXPECTED: Failed to get engine data from Remote Settings
console.log: "[OSK Manager]" "Character count is the same. OSK state unchanged by file read."
JavaScript error: resource://gre/modules/SearchService.sys.mjs, line 1319: Error: SearchService failed while it was initializing.
JavaScript error: resource://newtab/lib/TopSitesFeed.sys.mjs, line 141: NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS: [JavaScript Error: "SearchService failed while it was initializing." {file: "resource://gre/modules/SearchService.sys.mjs" line: 1319}]'[JavaScript Error: "SearchService failed while it was initializing." {file: "resource://gre/modules/SearchService.sys.mjs" line: 1319}]' when calling method: [nsISearchService::defaultEngine]
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_READ_CONFIG_COMMAND' command to OSK Manager."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_READ_CONFIG_COMMAND"})
console.log: "[OSK Manager]" "Character count is the same. OSK state unchanged by file read."
console.warn: "Access attempt to RS collection \"main/search-categorization\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/urlbar-persisted-search-terms\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"blocklists/gfx\" from local dump was blocked/filtered."
console.log: "[OSK Config Trigger]" "Dispatching 'OSK_READ_CONFIG_COMMAND' command to OSK Manager."
console.log: "[OSK Manager]" "Message received by Manager, Data: " ({type:"OSK_READ_CONFIG_COMMAND"})
console.log: "[OSK Manager]" "Character count is the same. OSK state unchanged by file read."
console.error: WebExtensions:
  Message: [Exception... "Failed to get engine data from Remote Settings"  nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)"  location: "JS frame :: resource://gre/modules/SearchEngineSelector.sys.mjs :: getEngineConfiguration :: line 100"  data: no]
  Stack:
    getEngineConfiguration@resource://gre/modules/SearchEngineSelector.sys.mjs:100:24

Crash Annotation GraphicsCriticalError: |[0][GFX1-]: RenderCompositorSWGL failed mapping default framebuffer, no dt (t=14.6022) [GFX1-]: RenderCompositorSWGL failed mapping default framebuffer, no dt
console.warn: TopSitesFeed: Failed to fetch data from MARS server: NetworkError when attempting to fetch resource.
console.error: "Error in processing browser-idle-startup for QuickSuggest.init"
console.error: (void 0)
JavaScript error: resource://gre/modules/ExtensionCommon.sys.mjs, line 2734: Error: listener not re-registered
JavaScript error: resource://gre/modules/ExtensionCommon.sys.mjs, line 2734: Error: listener not re-registered
console.error: SearchSettings: "_write: Could not write to settings file:" (new Error("cannot write without any engine.", "resource://gre/modules/SearchSettings.sys.mjs", 328))
JavaScript error: resource://gre/modules/CaptiveDetect.sys.mjs, line 20: :

from this the most important part is:

console.warn: "Access attempt to RS collection \"main/search-config-v2\" from local dump was blocked/filtered."
console.warn: "Access attempt to RS collection \"main/search-config-overrides-v2\" from local dump was blocked/filtered."

how i know it is this, if I remove fx-autoconfig I have search engines, if i load it without any JS or CSS file it doesn't work.
the log provided has some userchrome.js scripts but I tested without them the same will happen.

this is running on LibreWolf.
this is both a permission problem and a race condition between fx-autoconfig and LibreWolf's hardening I think.
if you want to see the full environment in which I ran this checkout uWolf It's a Wrapper for LibreWolf that adapts it to mobile for running on Ubuntu Touch.

EDIT: (narrowed down)
this bug, manifests in a very specific circumstance of fx-autoconfig trying to load config.js when there isn't a profile.
removing this line from config-pref.js fixs it: pref("general.config.filename", "config.js");, I tried slowly commenting out every line of code in config.js, but no its the act of loading it that does it.

this manifests in config-prefs.js loading config.js which somehow makes search engines not download.

[MrOtherGuy]

This is essentially the same as described in issue 54

The tld;dr is that Librewolf uses autoconfig for its own purposes and thus try to load fx-autoconfig will break theirs. You can probably merge the two files (as described in linked issue) but an update to Librewolf will likely undo your custom changes.

[ChromiumOS-Guy]

well good news, for my specific setup I load and change these files on compiling my wrapper, so really when users want to update they have to wait for me to update the wrapper (I have automation set for that, so really they don't), but the point is for my extremely specific use case undoing won't happen because LibreWolf can't update itself I update it.
anyhow thanks will implement in next version, I did implement a "fix" explained in detail here, warning read for amusement and horror.

[ChromiumOS-Guy]

i have this code do that:

/bin/echo -e """\n=================================\nSTART OF FX-AUTOCONFIG CONFIG.JS\n=================================\n""">> $INSTALL_DIR/bin/librewolf.cfg # make some space (the start/end \n is very important)

/bin/cat $fxautoconfig_dir/program/config.js >> $INSTALL_DIR/bin/librewolf.cfg #inject loading script into Librewolfs own.

this is what happens in librewolf.cfg:

rest of cfg

=================================
START OF FX-AUTOCONFIG CONFIG.JS
=================================

// skip 1st line
try {

  let cmanifest = Cc['@mozilla.org/file/directory_service;1'].getService(Ci.nsIProperties).get('UChrm', Ci.nsIFile);
  cmanifest.append('utils');
  cmanifest.append('chrome.manifest');

  if(cmanifest.exists()){
    Components.manager.QueryInterface(Ci.nsIComponentRegistrar).autoRegister(cmanifest);
    ChromeUtils.importESModule('chrome://userchromejs/content/boot.sys.mjs');
  }

} catch(ex) {};

now librewolf says Failed to read config file.

[ChromiumOS-Guy]

oh shit, just realized why its not commented.

[CosmoCreeper]

Librewolf documents an overrides file that you can add as ~/.librewolf/librewolf.overrides.cfg I believe. This means you won't need to configure anything, just add this, unless of course, Librewolf enables the sandbox, in which case you would just have to disable it with config-prefs.js and leave the rest alone.