I don't want to be surprised by disabled addons after update. How to test whether any of my addons will become disabled before (!) installing an update of firefox? Currently updateing from 77 to 80, but question is independent from version number: a general answer is preferred, Thank you.
Now that the add-ons are using the webextension framework (which they have been for years now), it's rare that add-ons will be disabled. The only way I can think of that happening is if the add-on developer has manually specified that the add-on is not compatible with later versions, which is not the normal because the add-on features are carried over to the newer versions.
If you go to the add-on's listing on addons.mozilla.org and scroll down to the More information section on the left sidebar, you can click the See all versions link. This takes you to the list of versions that the add-on developer has published. If you look up the version that you have (it should just be the top one), it will tell you what versions of Firefox are compatible.
Most add-ons will just say "Works with Firefox XX.X or later", which no specific cut off version.
Hope this helps.