Make sure that you do not run Firefox in (permanent) Private Browsing mode.

• https://support.mozilla.org/kb/Private+Browsing

• Firefox > Preferences > Privacy: Use custom settings for history
• Deselect: [ ] "Always use private browsing mode"

I have never put the browser in "Private Browsing Mode" and don't even know how to do that. My 'Privacy' settings do not even offer the option you quoted. "Tell websites I do not want to be tracked" is check marked and that's the only reference to privacy that my computer's options show. Is that what you mean?

To see all history and cookie setting select:

• Firefox > Preferences > Privacy > Firefox will: "Use custom settings for history"

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

You can try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default values.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

Disregard the former reply that I originally left, in this spot and have deleted, as it doesn't apply any longer. I've detailed why, directly below... Thank you for your kind indulgence. This problem is really driving me batty!!  :-|

The problem recurred and after verifying I have no add-ons or extensions, since I don't even know what they are, much less know how to use them the "Safe Mode" process wouldn't solve the problem. But at least now i know that the "Clear Recent History," in the Tools tab, works intermittently, but just not consistently. And the "Form & Search History" with tiny box next to it is unchecked and inaccessible (blurred over) sometimes, then appears accessible and check marked on other occasions. A very strange phenomenon...

I have a Mac OS X 10.7.5 system and have no idea where to find the "Profile" to implement the other possible fixes. I am not well enough versed in the technical aspects of this computer to even attempt the frustrating and tricky task of deleting files I haven't a clue where to find unless someone can take me through the process step by step in layman's terms.

There is either a bug in Firefox 19.0, which is very possible considering there are quite a few people who have reported this problem, or perhaps my last update somehow didn't download properly. Is it necessary to trash my current 19.0 version in order to download Firefox, again, or would another download of the same version override the current one?

I'd like to see if that works to resolve the problem, but the first time I tried, a file that I couldn't open ended up on my desktop and I had to move it into the trash, not knowing what else to do with it. It didn't even show up in the trash when I did that???!!! Please provide easy to follow instructions on how to perform the downloading of another 19.0 version to replace my current one. Perhaps that will work. Thanks!  :-)