Is Firefox slow?  Try these fixes:

Disable Plugins

By default,Firefox comes with unnecessary plugins.  To disable plugins go to the preferences menu, and select ‘disable plugins’

Disable Extensions

Firefox may have unnecessary extensions installed, depending upon how heavy of an extensions user you are..  Extensions can be useful, but they can negatively influence performance of the browser.  To disable extensions, go to the preferences menu and disable extensions  1 by 1.

Clear Browsing Data

Firefox collects history and other information as you browse the web.  The history database is used to make Firefox much faster, but the database can also become very large and slow down Firefox.