"This is certainly a bug. It is not a targeted attacked against Linux users. Report it to Microsoft. Microsoft is just doing really shitty feature detection using User Agent strings instead of, well actual feature detection. I was able to reproduce the same result by setting my User Agent to Firefox 52 on Windows 98. If I set it to a "more realistic" user agent like IE 7 on Windows XP, it would actually redirect me to a busted page to upgrade my browser instead of Word Online. It appears if Microsoft cannot figure out your User Agent (including your OS as part of it), it gives you a busted experience."