firstly you check for updates then clear your history and cache.

 *   Go to about:preferences and in General, uncheck the box for Always check if Firefox is your default browser.

• Go to about:preferences and in General, go to When Firefox Starts and select Show a blank page.

After using Firefox for some time, it starts using a lot of CPU process or RAM. To find out the cause of the slowdown, first try restarting Firefox in Safe Mode. This will make Firefox run without any add-ons or plugins. To do this, go to Options (the three-line icon at the extreme right of the URL bar) > Question Mark > Restart with Add-ons Disabled.

Firefox will restart and display two options: Start in Safe Mode or Refresh Firefox. Choose Start in Safe Mode.

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-ram

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

https://support.mozilla.org/en-US/kb/firefox-takes-long-time-start-up

MemTest LAST UPDATED : 27/09/2013 Could you please run a tool from http://memtest.org/ in order to check the integrity of your RAM?

You will need a thumb or disk drive to install it on.

Hello ...

please go through this link:

Quick fixes if your Firefox slows down

thank you..

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?