Disclaimer: I don't know if this has any meaningful security effects. Read the replies below to check what people are saying/recommending before doing this if you're unsure. I haven't personally had any issues [that I know of] since doing this last year.

You might have noticed that when you browse Mozilla sites (e.g. the Firefox add-ons site) your installed add-ons don't seem to work. This is annoying as hell, especially if you have accessibility needs that are met by an add-on. But there's a way to prevent this from happening:

1. Type about:config into your browser address bar (might have to accept a warning message if it's your first time)
2. In the search bar of the about:config page, type/paste privacy.resistFingerprinting.block_mozAddonManager and set it to True
3. Type/paste extensions.webextensions.restrictedDomains into the search bar this time, and edit the entry to remove any websites on which you would like to have your add-ons work (I just removed 'em all)