Firefox’s removal of any mechanism to switch user profiles while it is running is just another symptom of its drive towards user-hostile, Fisher-Price interface design. You might want to consider changing browsers to SeaMonkey, which shares the same browser core as Firefox but uses a full-featured interface that is much closer to that of the Mozilla Application Suite (formerly Netscape Communicator) from which both browsers are descended. In SeaMonkey there is a handy “Switch Profile…” command in the “Tools” pull-down menu.
If you’re unable or unwilling to switch browsers, you might be able to live with creating desktop shortcuts that automatically invoke firefox.exe -P with your various profiles. If you also use the --new-instance option then you should even be able to run multiple profiles simultaneously. (I’m not sure if that option is present on Windows, which I presume you’re running, but it’s worth a try.)