Crashes or other problems with certain multimedia content in Firefox (such as Flash videos, animations or games) can often be resolved by performing the steps in these Knowledge Base articles:

• Flash Plugin - Keep it up to date and troubleshoot problems

• Adobe Flash plugin has crashed - Prevent it from happening again

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If the issue started occurring after upgrading to Windows 10 or after a Windows 10 update, please try reinstalling Adobe Flash Player.

I found the problem. As of yesterday, Firefox videos no longer work with Adblock. (They work when I disable Adblock.) So the solution is simple: permanently switch to Chrome, which plays all videos with Adblock.

You shouldn't have any issues with using Adblock and playing videos. Please ensure that you have the Adblock Plus add-on and not a fake copy.

Nevertheless, Mozilla does not develop or maintain add-ons, so you will need to get into touch with the Adblock team to advise them about the issue. You can also add the websites with issues to the whitelist.

Sorry for any inconvenience.