And yes, I have searched there are SOME similar items but not just randomly like this.

What was the CPU doing at the time? How obtain does this happen?

FredMcD said

What was the CPU doing at the time? How obtain does this happen?

Well, I had Firefox open and was browsing, and sometimes when I open a page in a separate tab it will do it. Sometimes when I just click on a link.

As to how often? Well, that is the whole meaning of the word in my post: RANDOM.

CPU was doing nothing special. It is a quad core Intel i5 And yes, I know Firefox is still stuck at 32 bit, but considering this will still alow 32 bit to have at least 3 to 4 GB of the memory that should also not be a problem. Total system mem is 16 GB. OK, I went slightly overkill on mem with the new machine.

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

FredMcD said

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Well, um, first this is NOT a bloody Mac. It is a Windows 7 Ultimate machine. And 2nd, this is so very random, and of course I must say I have been using these addons and keeping them up to date, and they have NEVER had issues. I already long got rid of those did cause issues. And kept only the ones that were PERFECTLY SAFE AND SOUND. And, again, I must iterate this is absolutely insanely random, there is literally no rhyme or reason to cause, just effect which is that Firefox stays in the task bar, BUT the window itself just vanishes for 1 to 3 seconds and there are NO errors reported anywhere at all.

CyberWolf64, does it happen in Safe Mode?

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.