Profile data can be removed or not recorded several ways;

• 1) Running Firefox in Private Mode (nothing is recorded)
• 2) Privacy settings; (Type about:preferences#privacy<enter> in the address bar.)
• 3) Many disk cleaners and anti-virus type programs can remove data from browsers. Open their settings and have them leave the browsers alone.
• 4) Mal-ware.

In the event that the passwords information is lost, you should record all information in a separate text file somewhere else on your hard drive, or written down. You can easily copy and paste if you need to do so. If you are concerned about someone else looking at that file, you can compress it using a password.

These can't get your data back, but will help in the future.

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backups of files that you choose.

OPIE {web link} Import/Export extension preferences

Have you had any kind of problems with the browser?

Have you noticed any pattern?

Look on your desktop. Do you see a folder called; Old Firefox?

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar. How many profiles are listed? How many should there be?

Do you have only one Firefox profile folder if you check that in the default location of the main profile folder?

You can use this button to go to the current Firefox profile folder:

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Go up one level to the "AppData\Roaming\Mozilla\Firefox\Profiles\" folder to check that.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\

"AppData" (XP: Application Data; Mac: ~/Library; Linux: ~/.mozilla) is a hidden folder.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

Firefox uses two locations for the Firefox profile folder, so make sure to look in the correct location. Location used for the main profile in "AppData\Roaming" that keeps your personal data.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\

Location used for the disk cache and other temporary files in "AppData\Local".

• C:\Users\<user>\AppData\Local\Mozilla\Firefox\Profiles\<profile>\

It has been this way every time a new update for a while now.Hopefully you will come up with a different solution.A window that flashes is not the way too go.I want to know and be able to control that due too the constant disappearing bookmark,passwords every update.I bet I spent more time fixing your problem with updates, then the actual updates.'Maybe 'this is related:Also My sling tv icon disappears and my background picture on main screen disappears,my login box on computer changes,but once I add my bookmark.It goes back to normal.

LXQMH7890 said

A window that flashes is not the way too go

What do you mean by this?

How often does this happen? Same time? Close/open browser?

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.

There is one profile listed there should only be one correct?

Never seen this window,If you have a window that flashes for twenty seconds that says your computer will stop working,if you don't push the button wouldn't you want a little bit of time.I would say a window that stay open until you install is much more effected cause it gives you a chance to react to the changes or even just a message in the browser itself .I Other browser don't install things that have the potential too be so damaging or require a large amount of time to fix.I tell you there are 10 bookmark save and I have to find the right one each time there is a download.

LXQMH7890 said

There is one profile listed there should only be one correct?

That is correct. Some users make use of more than one, but most users just use one.

LXQMH7890 said

Never seen this window,If you have a window that flashes for twenty seconds that says your computer will stop working,if you don't push the button wouldn't you want a little bit of time

Is this a Windows alert? A Microsoft update gives you time to decide to reboot then or later. Can you get a screenshot of it?