See if clearing cache helps:

- press Ctrl-Shift-Delete (Mac: Cmd-Shift-Delete)

- set 'Time range...' to 'Everything'

- untick all items except 'Temporary cached files and pages'

- clear, then restart FF

If that doesn't help, click the padlock to the left of the address bar > Clear cookies and site data > refresh the tab.

Thanks Ed, for the very clear instructions.

I'd not seen those methods for clearing cache before.

However, having run through both sets of instructions, and restarted Firefox twice, the problem still remains.

It's a head scratcher. Everything was fine before I went away for a week, and when I came back, Facebook on Firefox was originally OK, but then it started playing up.

So I'm still looking for a solution.

Well would you believe it.

I tried it one more time, and it worked.

Thanks Ed for all your help, much obliged.

Well would you believe it. I tried it one more time, and it worked. Thanks Ed for all your help, much obliged.

You're welcome :-) I think that was actually a FB bug making the rounds.