Mozilla has been the leader of Open Source projects from the beginning, and with products like Firefox, it has already given tough competition to its competitors including Microsoft, Apple and Opera. In general, these companies are not competitors of Mozilla – as they don’t share common objectives – still if you consider competition among the browser vendors, Mozilla is a clear winner. So far so good. Google enters in the scene. The world changes.
Google is not a company similar to MS and Apple. Google has a great history of supporting open source and open standards. Chromium (Chrome) is just one example of this. Currently, Google is using all its existing powers to promote Chrome including via its services and advertisings. This is the reason, why Chrome is not just another browser or an easy competitor for Firefox.
Mozilla’s Gervase Markham has listed three main competitive advantages for Mozilla on his blog. These are open community support, ideals and goodwill. Gerv reminds, "Hard numbers are difficult to come by, but the often-quoted figure is that 40% of the Mozilla codebase is contributed by people we don’t employ. However, that doesn’t count the massive efforts people put in doing QA, documentation, support, local activism, and encouraging their friends to download, install and use Firefox.". You must read his post here.
A commenter on his post points out how Mozilla is more open than Google/Chrome, "Mozilla doesn’t include closed-source binary components in their browser (e.g. Chrome’s internal PDF reader) and doesn’t back problematic codecs because it’s convenient (Chrome still ships a H.264 decoder despite Google’s announcement to remove it).".
Keep it up, Mozilla! :)