Yes, I agree Firefox has become sluggish but then again we are asking lots of our webrowser now. The answer probably is Chrome (Chromium in my case, linux etc) - or architecture like it. We all love tabs, the problem is Firefox has them all in one job, now Chrome is smart and each tab is actually a separate thread running on your machine and thus is much faster. For Mozilla todo this will involve a serious rewrite. We all have multi-cores these days and so this nicely distributes the load.