I don't think anyone begrudges Ubuntu taking advantage of a perfectly acceptable revenue model. That's not the problem here.
The problem is that Ubuntu is shipping a modified version of Firefox instead of the default Firefox shipped by Mozilla. Sure, both Ubuntu and Debian ship patched versions of just about every package they include in the repository. But the overwhelming majority of those patches don't noticeably effect the user experience.
Firefox, on the other hand, is pretty much the #1 most important part of the user experience in Ubuntu. It's the application most people are going to use more than anything else. In fact, after Ubuntu is installed, the user will probably spend more time interacting with Firefox than with all the rest of Ubuntu combined. It's not inaccurate to say it's a Firefox machine, as opposed to an Ubuntu or Linux machine.
Since Firefox is the most important part of the user experience, the users don't want Firefox changed in any way. They want the default Firefox as shipped by Mozilla. They don't want the named changed to Shiretoko or IceWeasel. They don't want the icons changed. They don't want weird extensions that change behaviour. They also don't want updates to come from Ubuntu repositories, as they do for every other package. They want the newest version of Firefox from Mozilla at the exact moment that Mozilla ships it.
I understand the reasoning behind Ubuntu and Debians policies, but I think it is obvious that Firefox trumps Ubuntu. They should make a special exception for it. Just ship the raw Firefox as released by Mozilla. Don't modify it in any way whatsoever. The world is just getting more browser centric. The operating system is just the code that talks between the browser and the hardware. You can do anything you want to the OS, but don't touch the browser or you'll lose all the users you worked so hard to gain.