Well yes, the warning messages will disappear as those are often shown or not shown based on user agent.

But will the actual streaming issues go away is the big question.

Teams on the web for example, worked fine in Firefox even though it warned the user it didn't work in anything but Chrome.

Pretty sure Firefox added support for HEVC a while back, but it relies on the system to provide the decoder (Which you'll usually have to pay extra for)

Firefox also supports MKV files now, which is nice.

Tell them to get their shit together and support open-source browsers, or more accurately just browser standards in general.