10
Can't uncheck an option in firefox settings.
(sh.itjust.works)
Set your default browser to another one, then it should be clickable again
I suppose that is because you have to have a default browser. Well, strictly spaking you don't, I suppose, but some things are going to stop working.
It's not up to Firefox to scan your system for a list of browsers to offer you, so I suppose this is the easiest way.
As someone else said, just open up the browser you want to be default and check the option there.
A place to discuss the news and latest developments on the open-source browser Firefox