Firefox 90.0: No Internet connection under Ubuntu 20.04 LTS and Windows 10

Today, Firefox 90.0 suddenly stopped working under Ubuntu 20.04 LTS and Windows 10 as well.

At first, I was using Firefox 90.0 under Ubuntu 20.04 LTS and it suddenly stopped working. All other software programs could still access the Internet but Firefox 90.0 not anymore. Right now, I am writing this post using the Tor Browser (10.5.2 (based on Mozilla Firefox 78.12.0esr) (64-bit)) under Ubuntu 20.04 LTS.

I then restarted my computer using Windows 10 this time. Firefox worked for about five minutes and then it stopped working just like under Ubuntu 20.04 LTS.

Does anyone know what the problem might be? I have tried several solutions but none of them have worked so far.

We tried 3 approaches:

• Checking the output of netstat to see if some connections were failing to reach the remote server (e.g. TIME_WAIT state)
• Opening Developer Tools (F12) and checking the Console tab
• Opening Firefox Task Manager (for example typing about:performance into the address bar). This one showed some addons as "busy" and one of them was causing the problem