See:

• http://kb.mozillazine.org/Corrupt_localstore.rdf

Which security software (firewall, anti-virus) do you have?

Some security software has virtualization features that can cause problems by protecting and restoring files in the Firefox profile folder.

I use PC Tools/Spyware Doctor with Anti-Virus, latest version. Same product used on Windows 7 and Windows XP Professional machines. Problem only occurs on the Windows 7 machine.

Is it OK if you close Firefox and restart Firefox after having waited a short while to give Firefox enough to close down properly or does that also give the problem?

Did you try to delete the localstore.rdf file?

You can make a backup copy of localstore.rdf and compare the file date and file content of the localstore.rdf file the next day to see if it still is the same file or that is has been replaced.

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

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder

Closing Firefox, and restarting it even after several hours, is okay. Can do this several times per day without problem. Problem only seems to return on the first restart of the following day, and will continue to occur until I manually restore the menu bar and window size/aspect I prefer.

If I understand correctly, you are suggesting that I make a backup copy of the localstore.rfd, delete the original copy from the profile folder, and see what happens when I restart tomorrow. I have done the backup/delete, and will revisit tomorrow.

Does it also happen if you reboot during the day?

Okay, it appears that localstore.rdf is updated (or newly created) everytime I open Firefox. As suggested yesterday, I have backed up localstore and then delete the original. Today I captured the newest copy. So now that I have two copies of localstore.rdf, how do I compare the file content ? What application allows me open the file ?

Then, to the most recent suggestion, I have shutdown and rebooted my machine several times. Once I have set the preferred window size and toolbar arrangement on the first-of-the-day Firefox startup, that preferred setup persists across the several reboots.

You can't compare different localstore.rdf files as the order may change and new data added with saving data in a new copy. You can only verify that the file hasn't changed (i.e. has been modified or replaced by other software) since you last exited Firefox and Firefox saved its data in localstore.rdf.

So I have observed that it always seems to reflect a new date/time whenever I restart Firefox. But that also seems to happen on my XP machines without exhibiting the problem I observe on my Windows 7 machine. Any idea where we go from here ?

You need to check out the file before starting Firefox, because if you start Firefox then Firefox may create a new file and then you no longer have the original file.
The point is if the localstore.rdf file has changed between the last time you closed Firefox and the next day after booting the computer and starting Firefox on that new day.
That can happen if other software restore or removes the localstore.rdf file.

Okay, I have followed the path to the default profile folder using the Windows 7 version of Windows Explorer (or whatever they now call it). I did that with Firefox open and configured to my preferred toolbar and window size/position. I've noted that when I "Exit" Firefox, the time stamp on localstore.rdf gets changed to current time. I have noted that time and captured a copy of that file.

I will not use that machine any more today. Tomorrow morning I will check localstore.rdf before I do anything else to see if the time stamp has changed.

Is my process correct so far ? If so, and I find the time stamp has changed, how do I proceed to identify the source(s) of the change ?

Yes, that would be the way to proceed.

Cutting right to the chase, I now believe my problem is caused by a scheduled software event that runs overnight, and which deletes the localstore.rdf file from the Firefox profile folder. The reasoning is described below.

Today I followed the path to the Firefox profile folder. The time stamp on the profile folder indicated that its most recent update was the previous midnight. When I opened the profile folder, the file localstrore.rdf was missing. I started Firefox, which came up in the usual "default" config (square window on left side of screen and no Menu toolbar) Subsequent restarts exhibit the same configuration. If the backup copy of yesterday's file is copied back into the profile folder, subsequent Firefox restarts exhibit the preferred configuration.

Working Hypothesis: The problem comes from PCTools Registry Mechanic, which is scheduled to run a scan every night at midnight. To my knowledge, this is the only scheduled event that explains the midnight update of the profile folder. To test this hypothesis, I will cancel tonight's scan and see how Firefox behaves tomorrow. Stay tuned.

Working hypothesis is confirmed. The problem is caused by PC Tools Registry Mechanic. When it does a registry and privacy scan, one or the other of those scans causes the localstore.rdf file to be deleted. Recall that this only happens with my Windows 7 machine (never with my Windows XP machines). To the extent that we know the cause, this problem is solved. When I figure out how to make Registry Mechanic behave itself, I'll post it here.