I found that after Firefox v29, a LOT of my settings and
add-ons were changed / reset. Try this;
Start Firefox in Safe Mode
While you are in safe mode;
Firefox Options > Advanced > General.
Look for and turn off Use Hardware Acceleration.
Then check ALL of your settings. Browser and add-ons. Then restart.

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FEBE(Firefox Environment Backup Extension)
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 extensions individually into installable .xpi files.

It will also make backup of files that you choose.

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I with I could help you with the corrupted files. Sorry. :-<

"It resumed working one day later with a 1,7 MB file that contains the folders I'm looking for."

First, do you still have that backup? If so, I'm wondering if you would be able to see your bookmarks by adding the 1.7 MB backup to a *new* profile. (I'm suggesting a new profile because it's better to tinker with a new, temporary one than to risk damaging the main one).

What I still need to know is if there is a way to combine two different bookmark backups.

I do have an older .json file with all my bookmarks, including the now empty folders. And one from a few days ago (which includes all my new bookmarks since the older, larger .json file).

Any idea?

I have a thought. I don't know if this will work. Using a new profile, to prevent problems with your normal profile, load one of the bad files. Then <Shift><Control> B to open the bookmarks main window. At the top of the page, select Import And Backup. Then press Export Bookmarks to HTML. Then after, clear the system and do the same with the other bad file(s). The reason is you should be able to combine the HTML files later,

This is a very good idea (thank you!), but it worked only to an extent.

I imported both bookmark files. But how can I merge these bookmarks now?

I tried replacing older bookmarks with my newer ones like I would with a typical drag&drop. But they don't replace the older ones, but are just arranged after a diving line. Thus, most bookmarks are duplicates now. Any idea how to work around that?

That's the same train of thought I was on, fred. :) If max can access those bookmarks, he doesn't even need to export and combine anything.

Just copy paste from one profile to another:

1. http://i.imgur.com/rjOAZxx.png

2. http://i.imgur.com/u8JJMhx.png

3. http://i.imgur.com/i7iLlAo.png

• Bookmark Deduplicator: https://addons.mozilla.org/firefox/addon/bookmark-deduplicator/
• Bookmark Duplicate Cleaner: https://addons.mozilla.org/firefox/addon/bookmark-duplicate-cleaner/

I found a solution, thanks to melakopf who led me to think about it again.

I reimported my older backup and just sorted my newer backup by "last added", put them all in a folder and copied them. Worked for me.

Thanks to everyone who answered. You were very helpful!

My places.sqlite file was corrupt. I could not add/change or delete bookmarks. I also didn't have any backup bookmarks for reasons I won't go into right now. Nothing I tried would fix the file but one thing. Ironically, I used Google Chrome to import the bookmarks, then I exported them from Chrome to an html file. I deleted the places.sqlite file and imported the html with Firefox. All I had to then do was some rearranging to get things back like they were. All is good now :)

paulrevere You should make backups for this reason. If you want to keep the backups secure, take those files and compress them with a password.