[emanreus]

> flags the user as interesting/has something to hide (i.e. they are probably using Tor Browser, not just Firefox).

Tor nodes are known and it's trivial to detect users using Tor.

> There's also usability to consider - if this results in more people using Tor Browser, or not disabling things to try and work around it, that might be a net gain.

I'm sorry, but that's just ridiculous. Sharp corners on tabs most certainly won't attract more users.

EDIT: Ok I saw the issue with mobile users and some other edge cases. I would still agree with bo1024, it's a weak argument.