Azerus will be a massive system hog, depending on how connections and ports you allow, especially for programs like Firefox. You can expect your download and browsing speeds to suffer considerably if you use Azerus at the same time, depending on your connection.
Try going into the Azerus config and cutting back on the amount of connections it allows, then re-trying it. If that doesn't work, un-install Azerus and try and different BitTorrent client, such as U-Torrent. If that solves that problems, then its possible your version of Azerus was infected.