I really like this extension and its really vital to me.
Unfortunately Firefox has migrated to Webextensions and that together with a bug in Firefox has made the life difficult for the developer.
I understand the complaints since the black background on non active tabs make it impossible to read the text, but I also appreciate the developer to try and fix this this the best way he can with the tools he has available.

Please support the developer so he/they can continue to work on this addon.