There's such a marginal difference between the quality of the two browsers, and Chrome is held back in what it can be by the necessity of furthering Google's commercial interests. The only limit Firefox has had is that they can't abuse the trust of their users. Firefox had to voluntarily (and often aggressively) inflict a huge amount of reputational and functional damage on itself to reduce its market share to the place that it has.
edit: it's important to say that they didn't really backslide technically; it's user-hostile (management) decisions that have hurt the browser, not anything to do with the skill of Firefox developers.
It is questionable, and being declared a search engine monopoly would be far worse for Google than Chrome being a browser monopoly. They only make Chrome to push their search/ad network.