There are some disadvantages in using older versions, one problem is that with the faster release cycles (firefox 5 scheduled for full release next month - 24th June? ) you may find old versions are not supported as long as you expect. The last main change was from Firefox 3.6. see also [[installing a previous version of firefox]]. Firefox 4 is intended to be faster than Firefox 3.6, or are you only having problems with:<br/><br/> * slow startup, ( some extensions eg firebug slow down startup a lot) *only certain websites especially video or animation content, or when data/cookies are cleared <br/> (consider turning off hardware acceleration, maybe even the html5 parser feature, review the number of instances of plugincontainer that are open - bug opens them) *or when many tabs are open. <br> (consider bookmarking folders of tabs and not keeping as many open all the time) Firefox 4 seems to work ok for me so others may be better at explaining any problems with its speed.