In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Site Preferences

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/remove-recent-browsing-search-and-download-history

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data

Oops I was so sure that that would work I marked it solved, but...... drat, I had to install some updates and all my settings described above disappeared again, and Google fonts are at 9pt again despite that I have site prefs settings not emptied open closing FF....

Did you try to set the desired preferences again in case they were lost?

You didn't use the Refresh feature and have created a new profile?

When you use the Firefox Refresh feature then a new profile is created and some personal data (bookmarks, history, cookies, passwords, form data, tabs) is automatically imported. The current profile folder will be moved to an "Old Firefox Data" folder on the desktop. Installed extensions and other customizations (toolbars, prefs) that you have made are lost and need to be redone.

It is possible to recover data from the "Old Firefox Data" folder on the desktop, but be cautious not to copy corrupted files to avoid carrying over problems.

I reset it several times. It is probably either a W7pro update issue or a FF update issue, because it started in January. I did refresh then. No good. I even went back to FF v32. No good because some critical web services stopped working, so I did a Safe Mode Restore, But whatever had been tripped stayed tripped. It is getting to the point now that I hate computers and cell phones, and the havoc caused by updates, so much that I use them as little as possible!

Does this happen all the time or only at specific days or times?

Did you install cleanup or security software recently?

There is software like Advanced SystemCare with its Surfing Protection feature that can protect files in the Firefox profile folder against changes and there is cleanup software like CCleaner to clear specific data in browsers like Firefox. If you have such software then check the settings or uninstall this software.

It happens all the time now in the last 3 FF versions, and I am happy that at least I have the option to reset the permissions in the screenshot. I use just MS Security Essentials and no net network/remote etc.

Also my printer drivers were suddenly no longer correctly signed around this same time, and I did set more allows in the Services.msc module. Couldn't fix that either, because peripheral device manufacturers have taken these new driver requirements by MS as an opportunity to screw the consumer by not updating drivers for devices out of warranty. Everyone I know is going through the same crap and is ready to throw out all the tech crap. Certainly no one wants to buy anything new now.

This is all way too much info but to tell the truth, I have had offers on my trusty IBM XP I keep in reserve for emergencies like this driver crap, and the only computer I can still print off. I have a W10pro computer too and it is so slow and limited in devices and software that the OS will tolerate, I never use it. I'll probably will go Linux on it. I need to do actual work on these computers!