Make sure you are not blocking content.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

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 Tracking Protection 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: Tracking Protection {web link}

Barrie1933 said

When I use u-tube and I have a list of sites then at the bottom is a "more" button. In the past when I have activated this I get more sites to download. Now when I do this I get the spinning circle and then nothing.

Hello Barrie1933,

This is not a Firefox issue though : I have tried other browsers, and the same thing happens .....

If it's a real problem for you, you could post a question here :

https://support.google.com/youtube/?hl=en#topic=7505892

I went through some older (Google) threads and found a lot of the same complaints - no solutions were ever found, but somehow the problem 'solved itself' (till it came back again and the whole thing repeated itself).

Update :

November 29 - the "Show More" button works again (in Firefox and other browsers .... )

Mine came back automatically after some time