If you use extensions (Firefox/Tools > Add-ons > Extensions) that can block content (e.g. Adblock Plus, NoScript, Flash Block, Ghostery) then make sure that such extensions aren't blocking content.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Of course, I have already done all that. I should have said so. I give up. This forum used to be helpful, but now it's just a bunch of people spewing the same old links and bullshit over and over. Going to Chrome. At least it works.

Can you post a link to a page with such a not working video?

Is the site using the Shockwave Flash plugin to play those videos?

You can get a possibly colored Lego block icon on the left end of the location bar that indicates that Firefox is blocking a plugin.

• https://support.mozilla.org/kb/why-do-i-have-click-activate-plugins
• http://kb.mozillazine.org/Issues_related_to_plugins#Click_to_Play