When you open Zen you will see a blank page. On this page you cannot open any extension pop up (clicking on a extension icon).
This extension fix this: It opens a about:blank page, so you can open extension popups. If you open Zen truh a link the extension will not open the blank page.
Tested in Zen version 1.17.15b.
Warning
During the installation you will set a config (xpinstall.signatures.required) in about:config to false. Setting this will allow you to install extensions that are not signed by Mozilla Firefox. So careful what you install.
- Download the latest Release.
- Go to
about:configand setxpinstall.signatures.requiredtofalse. - To install the downloaded extension go to
about:addons, click on the cog wheel next to "Manage Your Extensions" and then "Install Add-on From File..."
This will open a file dialog where you select the downloaded extension (ZIP file). - On the pop up click "Add" to install the extension.

Note
Please note that you cannot set xpinstall.signatures.required to trueagain after installation or the extension gets disabled.