Not the add-ons that you install, but the plugins that are on your system.

Firefox v52+ disables all plugins except for Flash https://support.mozilla.org/t5/Common-Responses/Forum-Response-Firefox-no-longer-supports-NPAPI-Plugins/ta-p/1370454

https://support.mozilla.org/t5/Problems-with-add-ons-plugins-or/Why-do-Java-Silverlight-Adobe-Acrobat-and-other-plugins-no/ta-p/31069

Note that add-ons need to be kept up to date with the current browser.

I assume you mean that starting with Firefox 57 (anticipated mid-November), Firefox will no longer run "XUL" extensions, only extensions that use the WebExtensions interface.

Many popular extensions are in the process of being rewritten or have strong competitors. However, some popular extensions simply will not be able to be rewritten due to the fact that WebExtensions does not allow the deep access to Firefox internals permitted to traditional extensions.

DavidFMayerPhD said

Why should anybody continue to use Firefox if the add-ons are going to cease working?

Since there will still be add-ons, I think the question might really be whether some people will stop updating Firefox. If there is not a "good enough" replacement from a user's perspective, they might stick with either: (1) Firefox 56, or (2) Firefox 52 ESR (which gets security patches through next February or so). Other users might switch to a different browser that carries forward the older Firefox code so they can keep using extensions that are no longer compatible with Firefox 57+. I guess we'll see.

All of this is something of a work in progress. The WebExtensions interface is expanding and filling out, but some things may not be done in time. As the dreaded date approaches, I think there will be many people reporting on what's made the leap and what hasn't and what you can do if you can't leave those extensions behind. At this point, I think it's not that helpful to speculate, unless you were planning on developing one of those alternate browsers, in which case, better start soon. ;-)

I'm sure everyone has their own favorite extensions that do magic with Firefox. I was thinking earlier today that there are some great tools I'm going to miss, but I don't know whether they are deal breakers for me. As the time nears I will be thinking about the options in more detail. Until then, I've got lots of other problems to work on!

Anyway, this isn't really a support question. You could monitor the Firefox subreddit for passionate discussions about pretty much any changes to Firefox, and relevant workarounds: https://www.reddit.com/r/firefox/

Do you mean the end of XUL based extensions and the change to Web Extensions?

• https://wiki.mozilla.org/WebExtensions/FAQ
• https://blog.mozilla.org/addons/2015/08/21/the-future-of-developing-firefox-add-ons/
• http://www.ghacks.net/2016/11/24/firefox-will-only-support-web-extensions-by-the-end-of-2017/