It's about the EULA
That's the problem. Not the Firefox name for the program. Any program which is different from another should have some kind of different name so that no one gets confused, that's common sense and is basic programming etiquette among other things.
Normally you don't have to agree to any EULAs on Ubuntu, and this isn't some violation, it's because the normal license is all you need. There are no extra restrictions on the program past that point. Well, with the Mozilla license and Firefox, they apparently feel the need to extend an additional license right into your face which no one will read any way and they know it. It's just annoying and it's unheard of among most open source software. Like all the other normal licenses, you should only read it if you WANT to, in the help menu or whatnot, not have it shoved in your face, that's just annoying. But, if that's what they want to do, whatever, at least they only flash it once (so far), and not something really annoying like every time you start the program.
There are a dozen repackages of Ubuntu, including Linux Mint and Gnusense or whatever, so you can use one of those instead if you wanted, but it's still annoying that Mozilla is doing this, no matter how you look at it.