Perhaps these videos, audio or games are using a HTML5 player. Adobe made Flash EOL at end of 2020 so most current sites no longer use it.

Do you have FFmpeg and perhaps libavcodec packages installed?.

Patent and copyright restrictions are among reasons why Linux distros tend to not come with packages such as FFmpeg in a new install as it provides codecs needed to fully support HTML5 players.

If you are using a flavour of Ubuntu for example then see https://linuxconfig.org/ubuntu-20-04-ffmpeg-installation or https://help.ubuntu.com/community/RestrictedFormats

Or just install the FFmpeg package at least. Without FFmpeg, Youtube videos may appear to work fine however recently uploaded or live stream videos may not work depending on how they are encoded.

Youtube used to have a simple HTML5 test page to show if you supported all or only some of what youtube can provide.

Thank you for the reply. It looks like I do not have FFmpeg installed. However, what concerns me is why mozilla is bugging me with these messages when I'm not even trying to view a video.

Is there some background process trying to access video playing code (in which case, I should be concerned), or is mozilla just designed to keep pestering me until I install everything I'm supposed to?

Thanks

It looks like I do not have FFmpeg installed. However, what concerns me is why mozilla is bugging me with these messages when I'm not even trying to view a video. Is there some background process trying to access video playing code (in which case, I should be concerned), or is mozilla just designed to keep pestering me until I install everything I'm supposed to?

I assume it doesn't appear on boring sites like this one. Maybe it appears when the page has some cool video ads to show you? (But I run Windows, so don't have personal experience with Linux issues.)

Another message that comes up is an offer to install an outlook extension to my browser, but this is triggered by opening outlook email. I have no need for this either, so it would be nice to get rid if this message popping up as well.

Does this appear when you are using Outlook mail in Firefox? Sites can push a protocol handlers and trigger Firefox to display a bar that references adding an application. What that does it add a URL from the site for opening links with a specific protocol, such as mailto:bob@example.com. The URL is added to the handlers.json settings file and then becomes available the next time you click such a link. No extensions are involved.

Thanks for the response. So, I take the message that about the video codecs is occuring because of a background app that is trying to play videos, and there's nothing I can do about it.

As far as the second point, yes, it occurs when I open outlook mail in firefox. Whatever it is, extension or setting, I don't want it, and there seems to be no "don't ask me again" option.

On the Outlook, I am not aware of a way to suppress that message except to add it.