Well 3.6.28 is pretty old. I'm running Firefox 17.0.1. While I agree that updating can have it's problems - specifically, Windows updates - the only issue I've had with updating Firefox, is sometimes a plug-in you like isn't supported for a week or two until the plug-in catches up with the update.
Staying with a version as old as 3.6, you can run into compatibilty issues with other programs that are newer.