I get a Warning Unresponsive script error If Firefox freezes and gives you the spinning wheel and turns white gives you the spinning beach ball turns gray, try the Firefox hangs or is not responding - How to fix article. If a monitoring tool shows you high hardware resource usage, try the suggestions in the Firefox uses too much memory or CPU resources - How to fix article.
See your manufacturer's instructions on how to update your video drivers. Having outdated drivers might slow down performance. See Update Firefox to the latest release to learn how to update. The latest version is faster than ever before and contains fixes for many problems that could slow down your Firefox.