Try to disable hardware acceleration in Firefox.

• Firefox > Preferences > Advanced > General > Browsing: "Use hardware acceleration when available"
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I've tried this, which I included in "Have Tried ALL Given Answers/Solutions." None have worked so far.

So, even Safe Mode doesn't have any effect?

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

Correct: Safe Mode makes no difference. I think that I tried another profile, if I did it right, & no diff. Actually, I did this 1 better: I used a separate MacBook Pro (my wife's 2.8GHz Intel Core 2-Duo) running the same version of OS X 10.8.3, and the same version of FF (21) under her login, not mine, & I get the exact same result. IMHO as a retired I.T. professional, the problem lies within Mountain Lion vs. FF. I can run FF under a VMware partition using Win 7 Pro on my same MBP & get it to work just fine. I can't run it under Lion w/o a great deal of difficulty (on this same MBP of mine, 2.8GHz Core i7). I'd have to dig out the older HD & boot off of it. With the release of the next OS X likely imminent after WWDC, I see this as just going to get worse if it's not fixed ASAP.

Hello,

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thank you.

P. S.; Track Pad use has the same result as mouse use does.

Thanks, but no. This does not fix it. I covered that I tried this in the first sentence of my request for help:

"I have tried EVERY suggestion given for this problem, including Version 19, & NOTHING has worked!..." I believe that "EVERY" includes a FF Reset. The mouse interface was re-worked in OS X 10.8 Mountain Lion, vs. 10.7 (Lion) completely. I think that this is where the problem lies w/FF.