Mike, did you try Troubleshoot Mode? (which tests a bit more than disabling all add-ons does) Or tested in a brand new profile? (which tests a bit more than refreshing does)

Mike, did you try Troubleshoot Mode? (which tests a bit more than disabling all add-ons does) Or tested in a brand new profile? (which tests a bit more than refreshing does)

I've just tried both of those - didn't solve the problem.

Mike, did you try testing in a private window?

Did you try fully closing all Firefox windows inbetween the various troubleshooting steps, such as toggling settings, or testing in the clean new profile?

Mike, did you try testing in a private window? Did you try fully closing all Firefox windows inbetween the various troubleshooting steps, such as toggling settings, or testing in the clean new profile?

Yes, I've just tried all that - didn't solve the problem.

Additionally, I did a full uninstall and reinstalled an earlier version of Firefox (128), and that didn't solve the problem either. Have uninstalled that version and reinstalled the latest version, still have the same issue.

At this rate I might have to abandon Firefox for the time-being, which is a shame as I've never had a major problem with it before.

Mike, sorry but I am running out of ideas!

The last thing I can think of is to uninstall Firefox, move all left-over install / application data folders on the hard drive to a temporary location, and then reinstall.

If that doesn't work, and if no-one else has any other ideas, then you may wish to consider filing a bug report at Bugzilla: https://bugzilla.mozilla.org/home

I tried another uninstall/reinstall and moved all the related folders I could find. Still no luck.

Thanks for trying. I'll file a bug report, but in the meantime I guess it's time to go back to Edge.

Mike, sorry that I couldn't help. If you do go on to file a bug report, then could I ask that you post a link to it here, for reference? Thanks.

There have been a lot of reports recently of people having problems with video playback on sites such as Amazon Prime. So it might be worth using the Bugzilla search to see if any of the existing reports already describe the issue.

Mike, some people with these media playback issues have been helped by making a change in about:config.

If you want to give this a try, then see Paul's post here: https://support.mozilla.org/en-US/questions/1457849

Mike, Another thought, when a video starts without audio can you still nevertheless unmute it / raise its volume via its controls?

Also, what are your current autoplay settings?

Firefox can be set to autoblock audio while allowing video playback, so I am wondering if some setting has changed for some reason.

To check your autoplay settings you can do the following:

1. go to the Tools menu (alt+T) and select settings.
2. in the settings page, search for "Autoplay".
3. find the Autoplay section in the results and press its settings button.

First you may wish to note down the existing settings before making any changes, so that you can restore them if the following doesn't make things work the way that you want. Also, remember to press "Save Changes" and you may need to restart Firefox for the changes to take effect.

If the "Default for all web sites" setting is set to something other than "Allow Audio and Video", then try changing it to this.

Or if there is a website exception listed with a setting that is something other than "Allow Audio and Video", then try either removing this exception, or changing it to this.

Thanks, I just tried those last two suggestions and neither worked. Autoplay was set to 'Block Audio and Video' for all websites, but changing it, saving and restarting Firefox didn't solve the issue. No website exceptions are listed.

Just installed the latest Windows 11 update (KB5041587) and this seems to have resolved the issue - video and audio all working fine now.

Many thanks for your suggestions.