If one version a year is not enough for a browser (heck just look at Google Chrome) philosophy isn't just cutting it, then Mozilla is upping the stakes with a planned four major releases to bring the browser up to version 7 by the end of the year.
In their upcoming roadmap, Mozilla is doing away with its current production cycle of endless betas and seem to be going forward with a much faster release cycle, most probably influenced by the abovementioned other browser.
Good thing? Bad thing? You decide, but one thing is for sure, with another browser joining Chrome in updating so quickly, other browsers not doing so will look outdated by comparison.
mozilla.org - We succeeded in re-energizing the browser market, creating competition and innovation which benefits Web application developers and users alike. This newly competitive market has presented challenges for the continued success of Firefox, and in 2011 we must ensure that we can deliver a product that is compelling to users in order to continue to be able to demonstrate our vision for the Web. This roadmap outlines our planned strategy and direction for Firefox in 2011.
Full roadmap here and there's even a tl;dr just after the contents...