Fortunately there is another option. Copernic has recently announced that version 1.5 of its desktop search app will support not just Firefox but Thunderbird and Eudora too. Version 1.5 is currently in beta. PC Magazine has reviewed Copernic’s 1.5 beta and they were pretty impressed. They gave it a "very good" rating. I intend trying this out as soon as I get home.
You would have to have been living in a cave not to know that one of the big ‘New Things’ is desktop search following on from web search. There are a couple offerings available already. The better known applications are from Google, MSN and Yahoo (a free variant of the X1 desktop search application). Unfortunately many of these offerings don’t search all the files you would like them to, at least not the free ones (as I understand it, the paid version of X1’s desktop search app will search just about anything). This presents a difficulty for people who use Firefox and Thunderbird for web and mail, respectively.