Have you tried resetting things in Task Manager Paul?
When it locks up, do the ~ Ctrl-Alt-Delete all at once ~ option.
Select "Task Manager" at the options window.
Once Task Manager is open, find your Firefox and see how much resources it's using up. All of my browsers have some sort of issue rendering web pages at times, some much more than others. Facebook is extremely ugly, with all of the ads, and videos trying to preload/load. All of the clickbank webpages off of Farcebook are terrible as well. Woodbarter is actually one of the few pages that I seldom see trouble on, in fact it works flawlessly unless I have other pages open in the background. Preloading ads seems to be the culprit, the more ads, the more trouble I have, because my ad blocker holds things up, and I get stupid messages to turn my ad blocker off for better browser performance. Personally, I think they need to turn all the 87 friggin ads they're calling from other servers off, for better browser performance.
At any rate, find the FireFox line in Task Manager that's using up all the resources, there will be several, click on it to highlight it, (can be challenging it moves constantly), and click "End Task" bottom right corner. It will cause the web page to crash, (if it doesn't find another to click until it does), should give you a link to reopen the page, and you should be able to restart it, and run for a while, before it crashes again, although that's not always the case.
And, I've seen that in Microsoft Edge, IE, Slimbrowser which uses the IE browser engine, Commodo Dragon which uses the Chrome browser engine, and Firefox, 32 bit and 64 bit versions, so it's something deeper in the system that's controlling the rendering process on mine.
Ending the task and crashing the page, will however unlock the cursor, and restore function to the browser controls, so you can exit, or reload the page and carry on.