I remember when I installed Mint on this machine that Firefox 84.0.2 was the latest version available as the machine is only 32 bit. I don't think there are any updates to be had......
I am back in front of the machine, have been for a few days now, and the locking out issue seems to have gone away. The only change I have seen in anything is that the streaming video I usually keep an eye on has changed it's Youtube page. Previously, the live stream of the webcams at both Grosmont and Goathland stations (North Yorks Moors Railway) was a page that loaded the last 2 hours video when launched. Once loaded it then kept a 2 hour rolling buffer and allowed the viewer to click back and forth to watch any part that you want to replay. The link for that broke a few days ago and the page that is called up now doesn't allow user to rewind at all. If you miss anything it is gone for good. Perhaps there is something in the more user friendly page that is incompatible with the Firefox browser or inherently faulty.
Rans6..............