Mozilla isn't (currently) interested in countering the rise of Chrome or Safari. The Mozilla Foundation and the Firefox team are pushing for a more open, standards-driven web, and both Chrome and Safari are better than IE. Only after standards are really standard can you have a meaningful competition on the merits of various browsers.
Sadly, Firefox doesn't handle this properly natively. Happily, there's a plugin for that: https://addons.mozilla.org/en-US/firefox/addon/8207