if you directly downloaded the zip from codeberg (like this), that zip will not work
if you open that zip, there will be a folder inside. extract that folder to somewhere and zip it's contents (so when you open the zip it shows the .js files without needing to click a folder)
After that, change the extension to xpi.
Finally, before installing, you need to either
disable addon signature checks
about:config
-> xpinstall.signatures.required
= false
), will probably need firefox developer edition or nightly. beta might work toomake an unlisted addon on addons.mozilla.org to get it signed
After those, you can just drag and drop the xpi file into the extensions page and it should work
nice, a working fork for chrome too!
btw, you might want to pull this change from my fork to make subreddit comparions ignore capitalization. this is kind of a weird oversight where you have to exactly match a sub's original capitalization to get the tag to count.