If you can run two monitors you can use wow in windowed mode and not need to 'alt-tab' or otherwise minimize the warcraft windows.
You can obviously do this without two monitors and have quick access to firefox (or itunes, etrade, etc). There is a performance hit with windowed mode, but it does have dynamic fps (frames per second) to degrade game play video quality to compensate.
Issue with this is that if you are using two video cards, some video cards introduce some issues when you drag windows between video cards or span windows between two different video cards. This isn't an issue with Windows7 any longer.
You also likely want to adjust the setting 'play sound in background' as when you wow window doesn't have focus it won't play sound. So when your surfing wowhead (or stackexchange) you won't notice chats, yourself being attacked, ready checks, etc otherwise.