It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

Hi Fred, Thanks for your very detailed solutions to my Firefox issue. You correctly identified the issue as being the 'Hardware Acceleration' setting. I un-ticked the box, opened 20+ tabs and very quickly clicked between them. All was very stable and no sign (thus far) of the problem I was having. I want to give a you a heartfelt thanks for your help here. I had been stumbling around fruitlessly trying to solve this thing for quite a while. I can now revert back to a browser I have great affection for and trust in. Many, many thanks once again Colin

Glad to help. Safe Surfing.