Button to disable/re-enable syntax highlighting does not work on Thunderbird 91.

[Qeole]

The toolbar button to disable/re-enable highlighting does not work on Thunderbird 91.

This is apparently a regression in Thunderbird, see https://bugzilla.mozilla.org/show_bug.cgi?id=1722065.
The current plan here is to wait for a fix on Thunderbird's side.

Thanks to @fbezdeka for reporting the issue and finding the relevant bug.

[Qeole]

There is possibly a workaround here: https://bugzilla.mozilla.org/show_bug.cgi?id=1722065#c8 (might be needed for TB 93+, from what I read?), but I haven't managed to have it work yet. I'm getting a uncaught exception: Object, possibly when the button disappears, so maybe there's something else broken somewhere.