If I understand the question correctly, it's because Firefox is single-threaded. A better question might be why Firefox is single-threaded. Apparently it's som

If I understand the question correctly, it's because Firefox is single-threaded. A better question might be why Firefox is single-threaded. Apparently it's something to do with JavaScript. An even better question might be what connecting to a server has to do with JavaScript. I don't have a good answer for that. A quick search suggests that Firefox 4 will be multithreaded though, so you might be in luck.