The Tor browser is a modified version of Firefox, but you are not meant to modify the Tor Browser, in order for everyone using the Tor Browser to look the same and blend in. This is done for maximum privacy and anonymity.

It's not possible to identify you if you use the tor browser without changing the window size or any other settings, because the fingerprint is literally the same amongst everyone that uses it this way. So you kind of blend in with the masses, it's neither generic nor unmodified, I give you that :D

Simply the OS already makes that difficult, true. Nonetheless, it's one of your best bets.

For those who truly want to stay private, installing plugins on the Tor browser is obviously a no go. Changing any setting or even the window size should not be done. Seriously.

And I'd venture that Tor on phones might be the most homogenous, though that still isn't saying a lot, sadly. Plus, smartphones are a privacy nightmare regardless (tip of the iceberg).

In the end, fingerprinting makes true privacy very challenging. Great introduction to the topic.

And an advanced writeup with excellent resources for those who really want to get into the subject matter.

Edit: spelling