Yesterday I upgraded my Firefox browser to Quantum (version 57). I found some replacement addons to replace a couple of the ones Quantum disabled. Later in the day Avast Antivirus flagged two of them as having bad reputations and offered to remove them. I let Avast remove them, but all it seems to have done is removed them from the list of Extension on about:addons, the Firefox page where you add/remove/configure extensions. Is there another way to remove them?
Firefox 57 is almost a year out of date! For your own security you should update your browser (the latest is Firefox 63.0, released today).
You can remove the add-ons via menu: Tools → Add-ons → click Extensions on the left, find the offending add-on in the list and click the Remove button.