Weird. They claim Firefox is not supported, but with some user-agent switcharoo it seems to work fine.
Ugh.
Ugh.
It may or may not work, but since that is a bad user experience, they disable it.
"Supported" means that they provide a certain effort for make the configuration operational for their users, by designing said support if needed and providing assistance as required.
"Hey look, I can save my PowerPoint as a web page! And it even has the animations!" Except it's 2024, and we have standards, and for them to say, "Oh we don't adhere to the standards" is shockingly bad.