was working for 30 mins until I realised that Firefox was "stuck" and unclickable.

I had an issue like that come and go on Gnome (Ubuntu's default desktop environment) with Firefox and Chrome. I never tracked down a root cause.

I switched to KDE Plasma, instead.

I feel like Gnome is going through a finding itself phase, right now.

Edit: That's the beauty of open source. I can help fix the problem, or...if I can't....I can nope out of the way onto another solution until it is solved.