What did you try?

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

seems to have resolved itself. I had tried start in safe mode as outlined above - no better - hadn.t tried creating new profile

the problem is the flash player, not firefox. To fix the problem:

1. to go to a website that have a flash video, such as youtube 2. right click on the video then select "global settings", this will open up the flash player setting manager 3. click on the advance tab 4. under "browsing data and settings", click "Delete All".

that is it , u will notice firefox wil run smoothly once again. if after some time firefox slow responding again, just do the same thing to fix it. goodluck!!!