Hello Jhazel,

Would you please make sure that you're not in permanent Private Browsing mode :

3-bar menu (or "Tools") => Options => Privacy & Security => under "History":

Firefox will : choose "Use custom settings for history"

Uncheck  : "Always use private browsing mode"

Another thing that might be responsible for the problem : I noticed in your system details "Trend Micro Toolbar" (inactive). Even though in Add-ons => Extensions it is disabled; would you check to see if it's still in Windows Control Panel ? If it is : would you please remove it ?

Not sure exactly what fixed it, so cannot say how it was fixed, but: I have never yet used private browsing mode and the option was not checked. also, I did not find the Trend Micro toolbar on the Control Panel. However, I did find the Trend Micro Password Manager (which I did not want anyway) so I deleted that. I restarted Windows and then FF. The setting was 'sticky' this time. Thanks for the help - I learned quite a lot more about FF from your response and am very grateful.

Also see; https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

Note that you can only have one Password Manager active at the time, so if you have other Password Managers for Firefox on your computer then the builtin Password Manager will be disabled.

Thank you. Of course, I only had one password manager since I believed that to be the case. IMHO, "well behaved software" should not activate itself without Administrative (or Root) permission. I never installed a second Password manager (they 'helped' me by installing it as part of a package) and I never accepted the invitation to use it. Accordingly I wrongly believed that I would be nagged about installing it similar to being nagged to activate it. I guess it is like spam, pushing unwanted software will be around and just requires attentiveness and perhaps patience with dealing with sales policies.

The "Trend Micro Password Manager" is known to cause this issue, so if you have (had) this application installed then we advise to uninstall this application via the Windows Control Panel like you did.