It's true, yet I think it still needs to be done, even though I'm often among the complainers. The key is balance: advancing UI without forcing users that are looking for a solid consistent experience to beta test your UI ideas. Ubuntu is an example of a lot of really bold UI decisions, and I think they're too eager to force things on users. Ubuntu is in the tricky situation of making a product for "the hard-core" (Linux geeks) and "the noobs" (non-tech-savvy users wanting a free OS).
And the reason I like Firefox is because there's always a way to go back to the old behavior/UI without losing the benefits of the new underlying system. That is respectful to users, as opposed to the Chrome way where you take it or leave it at a corporation's whim.
Pushing the envelope in terms of interface is a really tricky thing to do. Each time you do it, there's a huge user outcry, and it does turn some users away or stops them from upgrading. I don't think the Firefox feature announced here will be much different.
People like things to stay the way the are used to. Unless there's a huge change and they can see how dropping their old habits all at once is somehow an advantage.
Gradually adopting improved versions of the most sensible Chrome features might sound like sound engineering, but due to these dynamics I really wonder if its a survivable strategy in the long run.
There were some UX mockups posted a while ago that looked far more ambitious. That's more like it.