Firefox 88.01 - No tabs can load

Windows 10 Home 20H2

Worked fine yesterday, opened firefox just now and no tabs will load.

I've checked Allowed Apps in Window Defender Firewall and noticed that 'Private' is checked, but not 'Public'.
I don't know what settings I had before and I've not changed anything myself.
Any idea if 'Public' should be checked and this is what is causing the problem?

- - - Updated - - -

I just started Firefox in Troubleshoot mode and all tabs loaded as they normally do.
So it could be an extension causing the problem.
What else is there to look into that can cause this problem?

Use the standard method of disabling a set of extensions and testing; until you locate the problematic extension.

I've sorted it.
The extension 'Windscribe' was the problem.