Firefox is the only browser other than Chrome (and derivatives) on their OS. The web is supposed to be multi-platform. I guess it isn’t that surprising that modern MS is happy to just live in Google’s ecosystem though.

> * Too few people use Firefox to access Office online, they don't care

It's pretty much the majority of their Linux users. Firefox is often the default browser on many distros due to the Chrome/Chromium data sharing concern.

> * Your organization is too small for them to care

Then why even have a business tier if not for the support?

The result of Microsoft's current stance is simply that users look elsewhere. I mentioned Overleaf, but Google Docs is also a solid choice. For local editing we are using LibreOffice.

> It's pretty much the majority of their Linux users.

Sure, but for heavy users of office 365, how many use Linux to begin with?

if they will lose data when you're on a rarely used browser, can you really trust them not to lose data in general?

"yes, your car exploded, but you were driving on a dirt drive way. it works just fine on the highway"