Got stuck in my add-on: Stylesheet not evaluated, script doesnt work, but doesnt throw either

Hi all,

when starting to create my first add-on, I got stuck with some strange behavior.
Hopefully it is not a bug in mozilla but just my noobish ignorance.
My hope is, someone spots my fault a lot faster than I can…

Got my extension code at:
Actually this commit is breaking it in my development environment (Firefox 83.0 on ubuntu Bionic/x86_64)

Expected result is, that after loading the extension the sidebar only includes the German text and button on yellowish background (as it was before the commit).
Current result is, that German and English text and buttons are visible on default background, like as if the stylesheet would not be aplied at all.

Any hint - also in regard to how I could inspect the sidebar DOM in inspector - is welcome.


Thanks, hans_squared. That page selection icon wasnt too obvious.

Got it solved…Alternate Style Sheets are a mess…when specifying two stylesheets with a title, apparently only the first non-alternate stylesheet is processes.