Let's step through a few of the common fixes for this sort of issue:

• Refresh Firefox - reset add-ons and settings
• Upgrade your graphics drivers to use hardware acceleration and WebGL
• Install all Windows Update
• Troubleshoot Firefox issues caused by malware

Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration. Then check ALL of your settings; Browser and add-ons.

Poke around safe web sites. Are there any problems?. Then restart.

Thanks, Tyler and FredMcD.

Tyler - I don't want to reset FF as it will delete my customizations. It took a long time to get it to look and work as I wanted. Drivers are OK. Windows Update is current. Using Malwarebytes and Avast anti-virus daily. No problems reported.

Fred McD - Use Hardware Acceleration was already unchecked. I don't know what you mean by: "check all of your settings; browsers and add-ons." What am I looking for?

As I said, there may be a problem using DNS with Firefox. (They haven't always been friendly.) I'll stop using DNS for a while to see what happens with Firefox and the Not Responding problem.

The problem continues...only worse. I downloaded and installed Firefox 35 today, which was presented as a security update. Firefox now stops working and sends a "Not Responding" message every 60-75 seconds. There are no other programs running. My concern that Dragon NaturallySpeaking may have been the problem is no longer a concern. I think FF is the problem and since this has been reported for a long time by a number of people, I hope the folks at Mozilla can find out what is going on. (I recently sent in my annual contribution to Mozilla, so I'm feeling a little pushy.)

Do you have plugins running on firefox that might take up some CPU? Check this. Also did you install a plug-in on firefox that might be a virus, these things could overload firefox with too much data and crash it. Check that.

Set All Plugins to Ask. Then restart. Any changes?

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose.

OPIE {web link} Import/Export extension preferences

I wasn't seeing any jump in CPU usage when I got a "Not Responding" message. But, I started the tedious task of disabling add-ons one-at-a-time. I think I have identified the culprit: a wonderful add-on called Greenhouse. When installed, if you hover the cursor over the name of any member of the Senate or House of Representatives at any website, a pop-up tells you who donated money to that person and also who donated money to his/her opponent. I uninstalled the extension and opened a dozen web pages without incident. So I think I have resolved this problem. I'll report back if not.

Thanks to those who responded.

P.S. My apologies for assuming this was a FF/Mozilla problem.

That was very good work. Well Done. Please flag your last post as Solved Problem so other will know.