YouTube was specifically designed so that feature only works with Google Chrome, since YouTube is owned by Google. The same issue is present in Microsoft Edge and Opera. It's not really an issue, more of a broken by design situation.

No, not just YouTube. Porn hub too. DO NOT Judge me .

I suppose it could be related to the recently added autoplay settings. Try unchecking the Block websites from automatically playing sound option in the Firefox settings and then restart Firefox to see if the issue is fixed.

If it works after that, you may need to add certain websites as exceptions in order to block autoplaying videos on other websites.

I can almost guarantee that you won't get the functionality you are looking for on YouTube, since I haven't been able to get the described functionality on anything other than Google Chrome, but other websites should work fine.

A couple of weeks ago, someone had a similar issue with a popular news website and it was related to the autoplay settings. My assumption is that it's the same case here.

Hope this helps.

useufofor said

when I use chrome to brows youtube, whenever I put the arrow on any video it will provide a short preview of the video. But I can't do that on Firefox. It is not just youtube, also some other video website. chrome always allows u to preview the video without actually click it.