Firefox also gets you more hooked with its add-ons. This is getting worse with time.

Little things can make a big difference & FF leads the way in little things. Big things (big add-ons like firebug or colorzilla) are obviously deal-makers, but the little things are big friction points.

For example, the main reason safari irritates me is that they don't have the bottom of the page chrome. I like to see the URL of links before clicking.