> I imagine the tricky bit is testing the audio/video parts – "does the video work reliably with multiple participants" or whatever is probably quite hard to entirely judge in an automated fashion.

I actually forgot that Teams has audio and video. You are right about testing those two, I don't have a good idea for that either. I would probably look into using a virtual cam, like OBS implemented one, and then just check the footage on the other end?

But honestly, Firefox usually just works.

I agree. Honestly most likely they don't have the resources, the management, the money, the development experience, the culture, the transportation, the air to breathe, the water to drink ro the food tør at to solve this immense problem. Most likely they never even heard of Firefox, Chromium, Puppeteer, Browserstack, Playwright, Selenium or the internet.