The choice of browser is certainly even more important than the choice of editor. Fortunately, it’s a little easier because there are fewer choices. Of course, you’ll want to test your pages on most major rendering engines to make sure they don’t have any design flaws that could affect any user group. Choosing a primary development browser will allow you to add all the tools necessary to diagnose and debug HTML code.
There are many solutions for performing multiple browser installations. Some programs can easily have multiple independent versions on the same operating system, while others such as Internet Explorer, which is tied to the Microsoft installation process, will require tricks (such as IETester) to keep older versions on the same workstation.
The ideal is to use virtual machines to perform reliable tests. The idea is to be able to run other operating systems emulated by host programs in the same work environment: VirtualPC, VMWare, VirtualBox, etc. These run disk images containing a complete system and allow you to be in a quasi-real situation, with the constraints and specificities of each of them in terms of font rendering, plug-in management (Flash, Java, Silverlight), whether for Windows, Linux or Mac OS X.