Firefox@Lemmy.ml: Is it possible to install Firefox addons in Thunderbird?
Thunderbird's addon store is very lacking to compare to Firefox. Are there even technical limitations to this if Thunderbird use Firefox / Gecko under the hood?
No, add-ons have a list of applications they support coded into them, and it wouldn't make sense for a lot of them to be interchangeable. You don't need adblock in Thunderbird, you need spam filtering.
MV2 extensions should work in Thunderbird without modification. I've made a couple of simple extensions that work like a charm in both Firefox and Thunderbird, but I'm not sure if more complex extensions would have issues. The documentation says thus:
Some information listed on MDN may not apply to Thunderbird and some API methods may not be supported. Each API page should include a compatibility chart and if that includes support for Firefox, it should work in Thunderbird as well.
Some MV3 extensions will not work in Thunderbird. See this page for list of missing functionality.
Most dont work but you can download the .xpi files from within the browser using the addon "extension source viewer" and then sideload in Thunderbird by "install addon from file".