firefox autoupdater 3.0.0.1 has hung around as an incompatible extension for ages. Is there any way to be rid of it?
This extension has bee listed as incompatible since version 4. There is no option to remove provided.
Opaite Mbohovái (1)
If an extension doesn't have a "Remove" button in the Extensions Manager (about:addons) then that means that the extension has been added by other software or hasn't been installed yet.
In that case you have to remove the extension from within the Preferences (Options) of that program.
You can also check the extensions folder in the Firefox Profile Folder to see if you can locate the extension in one of the folders there.
If the extension is installed in the profile folder then try to set the extensions.autoDisableScopes pref to 14 on the about:config page to see if that stops the message.