Why cant you run 2 simultaneous instances of firefox? What OS do you use at work?
I use Ubuntu Linux 8.04 with two LCD monitors.... I use the proprietary nVidia drivers which support two methods of dual-screen set-up. One is called TwinView which allows you to drag windows from one screen to another, this is useful for most operations though for one particular application that set-up is not acceptable. One of my software projects at work involves an application called 'Probe Version 2.0' which is used by our software developers to help debug our embedded system software... But when it is run in TwinView mode fullscreen then it splits the screen between the two monitors which is not the intended way it should run... So I always set up the nVidia dual-screen to run with two separate X servers, one on each monitor. You cannot drag windows from one monitor to the other, but you can run applications on either window. I usually run a Windows virtual machine or a remote connection to a Windows machine which I use for developing my applications on Windows. This set-up is acceptable for the way I develop software at work...
I should clarify that I certainly can open several instances of Firefox on one screen at a time... So as I said, I will use Seamonkey when I need to open a web-browser on the second monitor. I usually use this browser to maintain a database I keep of the development boards for our development group...