FYI Chrome has more options installed by itself compare to Firefox so it can play a more varied files or videos. Firefox has limited resources so they implement the best use of their Browser for everyone in general and that could limited playback compare to Chrome or Safari with has bigger support team that can implement more features that come with their Browser. Another is that you have adblocker or types that is affecting the playback and if case you need to disable all of them and turn on one bye one then disable and next to find the problem Addon causing playback issues and if so remove or disable it so the webpages playback correctly.

Maybe you need to install the Windows Media Feature Pack if applicable.

• https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows
• https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues
• https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox