Are there particular sites where this is a problem?

If you seen the circling loading arrow endlessly, this can indicate that an ad-blocker is preventing a pre-roll ad from playing. If you use any ad blocking extensions, you may need to create an exception for the video site or for its video-hosting server (which is not always the same address).

Or to rule out extensions as a possible issue, try visiting the page in Firefox's Safe Mode. That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled (your plugins will still work)

In the dialog, click "Start in Safe Mode" (not Reset)

Any difference?

Netflix and some other sites use Microsoft's Silverlight plugin. I don't see that one on your list. You can check on the add-ons page to see whether it is disabled or completely missing. Either:

• Ctrl+shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Plugins. The disabled plugins (set to "Never Activate") cluster at the bottom.

If you haven't updated Silverlight for a while, try the link above the list to visit Mozilla's plugin check site and get a link to Microsoft's current installer.

Of it it's completely missing, try: http://www.microsoft.com/silverlight/

Use the latest version of Adobe Flash Player released.

Hi herake, unfortunately, when you join an existing discussion the forum doesn't prompt you for a list of your add-ons and other useful information, like what site is not working for you.

Could you start a new question with your system details? Start at the following link. Scroll down past the suggestions to continue with the form (I think it has 3 different screens).

https://support.mozilla.org/en-US/questions/new/desktop/fix-problems

Before posting, please test the same sites in Firefox's Safe Mode. That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled (Plugins like Flash should still work)

In the dialog, click "Start in Safe Mode" (not Reset)

If that makes a difference, or doesn't make a difference, please report on that since it's one of the things people will suggest if you don't mention trying it.

Thanks!