Try to disable IPv6.

• http://kb.mozillazine.org/Error_loading_websites#IPv6

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

Thanks for your reply!

I disabled IPv6. Still very slow.

To get in Safe Mode, I clicked Firefox/Help/Restart with add-ons disabled. I suspect this was the wrong thing to do because “All add-ons have been disabled by safe mode.

Actually, I did not see any opportunity to click a RESET button on the Safe Mode start window.

When I first entered the above question, I think I had an opportunity to run some diagnostics. However, because my computer is so slow, I actually posted the question from another linux computer, so saw no need to run the diagnostics on that machine. How can I get back to those diagnostics

Thanks for your help

You only get the reset choice if you start Firefox with the profile that is marked in the profiles.ini file as Default=1.

You can use the Profile Manager to start Firefox with this profile to achieve this.

• https://support.mozilla.org/kb/Managing+profiles

Sorry for my denseness. But I do not understand what I should do regarding the profile manager in my efforts to locate the cause of the slowness of my browsing. By the way, I tried to automatically add the Troubleshooter. It is still "installing" after several minutes.