Google pays users up to $1 for downloading FireFox [via AdSense referrals] and the Google engineers have even written some great extensions for FireFox like the Toolbar, Google Notebook, Browser Sync and Blogger Web Comments.
Google's revenue comes primarily from its advertising programmes and same is the case with Mozilla who earns few hundred millions every year when people surf using FireFox and click on advertisements displayed on search results pages.
At the same time, it's a well known fact that Windows hosts file and FireFox extensions like Adblock Plus are bad for the Google economy since the more people know about these workarounds, the fewer the ad impressions thereby translating into lower profits for the search company and the associated publishers.
Now this may surprise a lot of people - though Mozilla earns millions from advertising revenue indirectly, they have included Adblock Plus in their list of most recommended add-ons for FireFox for users to block "intrusive advertisements" on the web.
Aren't they risking the revenue stream of their search partners and their own with such recommendations ?
As the Firefox base increases and more people start blocking online advertisements, the 200kb Adblock installer will have the potential to hit the bottomline of search engines and even Mozilla pretty hard.