Make sure you are not blocking content.

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

One issue that seems more common lately is Firefox's Content blocking feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Content blocking {web link}

Many thanks, we appear to be connected again!

Did you find the cause of the issue?

I'm not sure I found the cause but in the process of checking around, I noticed my browser had not updated to v67.0 so I ran the update and then looked at content blocking, which held no surprises, I restarted the browser and Teams did then load.

I suspect it was due to the browser not auto-updating to v67.0

Many thanks,

Firefox 67.0 was only just released on May 21

https://www.mozilla.org/firefox/67.0/releasenotes/

Crikey! Don't tell me that, I will get a nose bleed being so close to the front end of development!

The secret of good comedy is timing, perhaps a happy coincidence, thanks James.