”Webpage is slowing down your browser” This is the new way the browser tells you there is a problem with the script program(s). https://support.mozilla.org/en-US/kb/warning-unresponsive-script?cache=no

As for the script problem I've already tried resetting the value at 20. It doesn't help. But that's just one of the problems that I'm experiencing with Firefox. As per my original inquiry, it also still hangs and runs slowly despite a Firefox refresh last week.

I called for more help.

Start Firefox in Safe Mode {web link}

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

Start your Computer in safe mode with network support. Then start Firefox. Try Secure websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

I ran Firefox in safe mode as suggested. That seemed to do the trick, so I tried that leaving it that way for a couple days couple days to sure. Voila! FF is running very well that way now. So the problem must have been caused by a (currently disabled) add-on.

It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

FredMcD.

The problem appears to have been Hardware Acceleration. Since I un-ticked that Performance option a few days ago, the FF browser is once again been running at normal speed. Thanks for your help.

Glad to help. Safe Surfing.