A quick look at the XPI on AMO seems like it should work. I don’t use messenger.com personally, so I can’t really test the content script. However, at least the browser action seems to work.
You might want to try and debug your content script:
There’s also a bunch of unused files packaged in your XPI, background.js and a newtab folder.
It’s strange, i try to debugging, so i select keyboard event breakpoint to follow what’s happening but when i press a key down i see the path in the differents other extension but mine is like ignored, my code is never called…
I found my error a simple document.querySelector(‘div’)[0] which is undefined so no possibility to get the value of index 0 so my script just end and never execute ^^’.