The new Opera 9.5, released about a week ago, quite easily established itself as my default "home" browser. It is sooooo much faster than Firefox and Internet Explorer, especially when it comes to heavy web applications such as Gmail and Facebook (and doesn't hang either). And what's more, the Opera guys finally made the Alt + D keyboard shortcut focus the address bar as is in the other two browsers (stretching out to reach F8 was rather inconvenient. Happiness is in the small things, you know... :-) ).
Opera 9.5 also includes DragonFly, which is the more powerful successor of the browser's previous web developer toolbar - the Developer Console.
It seems that I will continue using Firefox at work because of Firebug and Chris Pederick's Web Developer Toolbar - they are simply irreplaceable.