Firefox 3.6 will be end-of-lifed on April 24th, 2012.
Anyone still using this version will be given the choice to upgrade or continue using the unsupported browser. Mozilla will no longer ship security updates for this version (currently 3.6.28). Any security vulnerabilities that appear after this date will go unresolved.
I hate people stuck with IE6 or even IE7, but I do prefer my "ancient" FF3.6. It's only been a year and they've stopped updating it. Going 'the Chrome way' isn't going to be a success for Firefox and they might just push me away.
Being a web developer, I have all major browsers installed: IE8, FF3.6 and the latest versions of Chrome, Safari and Opera. Of all browsers, I prefer the old FF with its precious add-ons: Adblock Plus, CacheViewer and User Agent Switcher. But Mozilla's decision is harsh and make me reconsider my default browser option.
Anyway, there's still five days to make a decision. If they roll out another minor update, it might take me a few months to consider switching browsers.
I'll keep you posted.