[The Australian Panther]

Those of you using Mozilla may have noticed that all your add-ons failed in the last few days. Most should be back on by now.

Here's what happened. 

https://blog.mozilla.org/addons/2019/05/04/update-regarding-add-ons-in-firefox/

Mozilla made a mistake and they are in the process of fixing it.
So don't try to fix it yourself, just wait for it to come back on. Mine already has. If you've been off the internet for a few days you probably haven't noticed. You might need to check your add-ons to see if they are all there.
 
If you use Firefox and are reluctant to switch, can I also recommend Waterfox, which is an independent build of Firefox and getting better all the time.
Info below pasted in from another blog
[I recommend the Waterfox Browser for people who get used to Firefox during the past years. In a way it_s the same kind of browser.

Once Firefox didn't support the 64-bit-systems (which I have since WIN 7 was published). Some expert developed a 64-bit Browser on the Firefox base. And this Browser is still alive, updated and worked fine.

Waterfox does not collect ANY telemetry, meaning you don't have to worry about any tracking or usage information about what you do inside YOUR browser. The only thing that Waterfox sends back is your OS and browser version to check for updates.

Waterfox is one of the few fully customizable browsers, allowing you to modify and extend it any way you please. You'll even find some of your favourite classic XPCOM add-ons ported over such as DownThemAll!, Greasemonkey and the like.]
I use them both.
https://www.waterfox.net/
Cheers!