MP4 file will not play
I am using jwplayer to play video. I have made mp4-files. They work fine in Explorer and on my Ipad ( and I think chrome ) but not firefox. I will not play. Why is this?
Alla svar (2)
It could be an add-on that is causing the issue. Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that turns off some settings, disables most add-ons (extensions and themes).
If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:
- Click the menu button
, click Help 
and select Restart with Add-ons Disabled.
If Firefox is not running, you can start Firefox in Safe Mode as follows:
- Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
When the Firefox Safe Mode window appears, select "Start in Safe Mode".
If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.
To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.
When you figure out what's causing your issues, please let us know. It might help others with the same problem.
You can open the Web Console (Firefox/Tools > Web Developer) to see if there are error messages about these media files.