If you do not see a Remove button for an extension, it was installed indirectly. In some cases, it can be removed through the Windows Control Panel, i.e., it is part of another program you installed. In other cases, you could track it down and delete it manually. But disabling the extension usually stops the pain, so you have to decide whether full removal is worth the extra effort.
1. Start FF in Safe Mode from the program folder( No Add-Ons or extensions will load)
2. Go to Tools drop down
3. Select Add-ons
FF will List all your Add-Ons and it will offer 2 choices for every add-on, Disable or Remove.
4. Select Remove and it will go away.
Plugins are Different
They are Not removed but put on a list as a Disabled/Blocked Item.
Here is the link to Blocked Items
These usually stay blocked until the author repairs or removes their software.
Some are set to never activate, some plugins have a selection box to Never Activate or they have ASK For PERMISSION to be loaded because they have serious security flaws..
If you click on something that is linked to a bad Plug-In item you normally get a pop up that says Blocked because of a Blocked Extension/Plug-In error message.
An example is yesterdays shut down of an Adobe update, the download contained malware used to hijack your junk and FB.