Firefox is slow – How to make it faster.
What good is that super fast Internet connection when your browser is running at dial-up speed? This article will point you in the right direction to track down and fix the problem. Of course, if you need extra help with any of this, we have a community of volunteers standing by. Note: The Refresh Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Consider using it before going through a lengthy troubleshooting process.
Read the solution at the source: Firefox is slow – How to make it faster – Mozilla Support Community