I currently use Mozilla Firefox version 3.6.28 and it's running really great on my laptop. That is the oldest version of Firefox so it doesn't consume a lot of memory in my laptop's RAM. If you want to get this version, you can go to PortableApps and search this query “firefox legacy editions version 3.6.28” then download it to your laptop. The good thing is, you don't need to install this software on your laptop. Once you run the file, it will prompt you the option to save the software on the specific folder as your desire. So you can keep it with your flash disc it you want it.