Well, I disabled Sync, and that didn't solve it, so Sync isn't causing the problem.

Now if you'll excuse me, I have to finish combing through every file I've ever deleted in IObit Undelete because ComputerWhiz apparently thought it would be funny to convince me to do a clean reinstall and lose all my bookmarks, settings, and add-ons.

Hi BrokenEye, the Clean Reinstall steps linked in the reply you followed do not include removing personal setting, in fact, they do not even include uninstalling Firefox, just deleting the folder of program files (which by default would be in your OS trash/recycle bin). Sorry if that was not clear.

@BrokenEye
All of the people helping you with this thread are volunteers.
We would like to be treated with some respect.
We do all that we can to try to help you with the problem that you are experiencing.

I do not appreciate your derogatory comments towards me.
Please treat all of the Mozilla volunteers and users with respect!

Quote: Please treat ALL of the Mozilla volunteers with respect!

That would be better worded with:

Please treat the Mozilla SUMO volunteers with respect!
Please treat everyone who posts on this forum with respect!

(there is no need to emphasize with ALL this way)

Well how exactly do you expect me to respond when I lose all my bookmarks and whatnot because of something you told me to do, without any warnings whatsoever? If you had merely not helped the situation, then yes it would be unfair of me to get angry. But you didn't merely not help, you actively made the situation worse. And if you're really as knowledgeable about the program as your position implies, then I have every reason to believe you did so knowingly and therefore deliberately.

I should not have to remind you that respect is something that is earned, not given, and by that same token, it is also something that can be lost.

I apologize for any trouble that me previous suggestion has caused.
Under no condition would I ever deliberately cause a user trouble. I was merely trying to assist you with your problem.
In most cases, this solution works and since we have attempted most other things, there was really no other option but to try.

I would like to personally apologize to you for any inconvenience.
I can understand your frustration and am truly sorry.

Thankfully, I was able to recover my bookmarks (and only my bookmarks) using iObit Undelete. I won't be able to recover anything else until my other computer gets back from the shop.

After backing this up, I tried doing another clean reinstall deleting just the Program Files and not the AppData. This did not solve the problem, although I'm unsure if this is because I didn't do a complete clean reinstall or simply because the solution doesn't work.

For this solution to work, you would also need to delete the application data. Although it is not certain that this will work, we cannot be sure unless the application data is cleaned.

I am glad to hear that you were able to recover some of your lost information.
Again I am sorry for any lose of data.

Hi BrokenEye, in relation to the last two posts, how did you restore your old bookmarks? If you used the Restore feature to restore one of the .json backup files into an otherwise clean profile, then I think that is a clean enough test to rule out personal data as the problem. If you copied an old places.sqlite database into your new profile folder, file corruption still might be a possibility.

As I mentioned before, I had to use iObit Undelete (part of a program called iObit Advanced System Care) to sift through an unsorted list of every file I've ever deleted until I found the bookmarks backup files. This took approximately an entire day. As in an actual entire day, not just the bit where the sun is up. Technically I restored every file that had "Firefox" somewhere in its original file location, but the backup bookmark files were the only ones that actually brought anything back.

Absolutely not. Deleting the application data is what made me loose all my bookmarks and settings the first time around.

If you backup your Firefox application data before you perform a clean reinstall, you can restore the data if the solution does not work.

Okay, now I'm confused. If I'm just going to be putting it back in the same place, why delete it at all?

This is a long thread now, and it could be time to recap what has been tried:

• Safe Mode: bookmarks were not spontaneously added in Firefox's Safe Mode, but the test might not have been long enough to know for sure that they are never added in Safe Mode.

• Disabling Extensions: none of the extensions was found to be responsible for the behavior or, more specifically, the problem occurred with each of the extensions individually disabled.

• Fresh Install: did the problem occur immediately before installing any add-ons or customizing settings?

• Firefox Sync disabled: it occurs on multiple systems even when not connected through Sync.

Other than some bizarre malware or keyboard malfunction, it's very hard to think of other causes.

If the application data is not removed, we can not ensure that it is not a corrupt or damaged file inside of your profile.

As I said above, you can backup the application data to an external devise (ie. USB, external hard drive).
This can then be restored if the clean reinstall doesn't work.

Alright, I've backed up the two AppData folders and done another clean reinstall. Since it might be a while before the problem occurs again and in the meantime I'd rather have everything running the way I like it, I'd like to know which parts of the AppData can I put back without potentially re-corrupting anything.

Everything inside of the application data can potentially be corrupt. That is why it is important to remove the application data when doing a clean reinstall.
If at all possible, could you keep Firefox the way it is after the clean reinstall? It would really help us to completely rule out the possibility that Firefox is corrupt.
Sorry for any inconvenience.

As said above, I am sorry that you lost your personal information from your previous clean reinstall.
I disclaimer has now been added to the clean reinstall page to prevent this from happening to future users.
Sorry about that.

Erm... hmm. I don't know. As I've mentioned previously, the frequency of the problem is pretty erratic and it sometimes takes a really long time to crop up again. So I may be going for several weeks without my bookmarks or any of my add-ons (almost all of which are there either for security reasons or to fix some internet problem that I find infuriating), which would be more than just a little bit inconvenient.

I think I'll wait a week or so with it as it is now (with only the AppData pertaining to add-ons and bookmarks restored) and see if the error occurs again before going that far

By the way, if its not too much extra trouble, could you translate the "Modified Preferences" section of the "Additional System Details" dropdown for this question into Person-Who-Knows-How-to-Change-the-Settings-but-Doesn't-Know-Coding Speak for me? I'm trying to get things back the way they were before the reinstall, and I can't remember everything. I thought that section would be helpful in that respect, but I don't really understand what its saying.

Hi BrokenEye, the modified preferences contain a mix of changes made through the user interface (e.g., checkboxes in the Options dialog, enable/disable plugins) and data stored by Firefox during normal operation (e.g., last update check, etc.). Do you have an old prefs.js file you recovered for comparison?