Currently Opera, because of inertia and laziness. Originally I started using it for the free VPN and internet hipsteryness of using a less popular browser (much as I'd like to pretend otherwise, the latter is something my brain finds very appealing). I have a proper VPN setup now, but I've procrastinated switching to Firefox because of the general inconvenience associated with any browser switch and the need to for a minor rewrite on a browser extension I wrote/use.