''Nonresponsive Script''

Question

Whenever I hit the Stumble! button and I go to a site, I end up getting at least 2 messages of "This Script is unresponsive would you like to stop it." the problem though is that it freezes my browser(Firefox) for a while. I have Firefox version 3.0.4 and I have tried to uninstall and reinstall StumbleUpon.Help Please!