You can either configure the Firefox settings manually or use FireTune. The difference is 30 minutes or more. Instead of having to tweak settings in ‘about:config’ manually, just provide FireTune with some basic details such as CPU speed and Internet Speed, and it will optimize your Firefox based on such input.
It is a portable tool for Windows only, just extract the content from the zip file, open the folder, and hit FireTune executable file. You can also optimize Firefox portable using this tool, hit Settings, select Type Of Firefox, and choose Firefox Portable.

Note: Make sure you have made the backup of Firefox configuration before tweaking it with this tool. Backup and Restoration of original configuration can be made from within this tool.
It is a portable tool for Windows only, just extract the content from the zip file, open the folder, and hit FireTune executable file. You can also optimize Firefox portable using this tool, hit Settings, select Type Of Firefox, and choose Firefox Portable.