Rated 5 out of 5 stars
I use ConQuery in Thunderbird so that I don't have to copy/paste searches into Firefox. Shadow912's version for Firefox 5.0.* works with Thunderbird 5.0 if you hack the install.rdf file. Although I use this ConQuery in Thunderbird I do not use it in Firefox 5.0. Instead, I use Context Search (https://addons.mozilla.org/en-US/firefox/addon/context-search/) because it offers more or less the same functionality and is kept up to date by its developer. Anybody desiring the functionality of ConQuery without all the hassles should look to using Context Search.