So, exercise caution when installing new add-ons in the future, and for now do this:

Uninstall Unused Add-ons

You might have installed an add-on because you thought you’d need it. After a few days, you stopped using it/needing it. And now it just loads and consumes memory every time you launch and use Firefox.

Go to Tools then Add-ons to see a list of your installed add-ons. If you see add-ons that you installed but never used, uninstall them.

Disable Rarely-Used Add-ons

And there’s another class of add-ons. Those that you actually use, but only very occasionally. Keep these, but disable them, so that they don’t cost you memory and performance.

Go to your add-ons list again, scroll through the list to see which add-ons can be disabled without affecting your daily browsing. I bet you’ll find plenty.

Disable them and restart Firefox. When you need one of these add-ons for the occasional task, simply open the add-ons list again, activate the add-on, and restart Firefox.

I know, it’s not as convenient as having the add-on constantly enabled, but if you’re suffering from poor performance, this will help a lot.

Now you have a leaner, meaner Firefox that works just like before.