If you're using Firefox on your Nexus 6, Nexus 9, or any other Android 5.0 device, you might experience issues playing video and audio on some sites. Most of these issues have been resolved on the latest version of Firefox. Just follow these simple steps.
I can't play videos.
This has been fixed on Firefox version 34. Follow these steps to update to the latest version. This issue has been resolved on your version of Firefox. If you're still experiencing problems, please contact support.
I can't play MP3 files directly on the Firefox for Android browser.
This is a known issue that Mozilla is trying to resolve. In the meantime, try downloading the MP3 file and play it on the MP3 player that comes with your device instead.