Does it happen in windows , linux or MAC ?

Windows XP. I've had no problems since I downgraded to FF 28 last summer. THis is the first problem and I've never had it happen before (been using FF since 2012)

every time i open it, it does an update to "this version" to check add-on compatibility

I strongly recommend you to update your browser because using a old browser cause much trouble and it is a security thread. And now for your problem, you can try to create a new profile. Follow these steps:

• Press Windows Key + R ( or click the Windows Start button and select Run... )
• In the Run dialog box, type in: firefox.exe -p
  • firefox.exe -p will bring Profile manager. If it doesn't open Profile manager rather show you the same error box, please restart your PC and then try this command.
• Click OK
• Click Create Profile in the Profile Manager
• Click Next and enter the name of the profile. (use any name you like)
• Finally Click Finish

i upgraded every time there was one to be had, and FF kept closing (multiple times a week) without keeping a "previous session", so I was losing all my web pages. FF changed platfrosm (maybe this is the wrong word) with 29, and that's when my problems began. So i went back to 28 and have had no probelms since last summer. NOW, your solution worked -- but despite saying (when I created the new profile) that all my information would be moved into the new profile, ALL MY BOOKMARKS ARE MISSING. I read how to restore them -- no backups came up automatically, so I found the last bookmark backup -- they are labelled JSONLZ4 files, but when I tried to restore it, it tells me it's an unsupported file type. These files are in owner/APPDATA/MOZilla/firefox/profiles/default. if the file i want is somewhere else, please tell me. the article on restoring bookmarks doesn't actually tell you where the JSON file is!

Have you checked this article: Recover important data from an old profile

I hadn't, no. Thank you! I copied the place.squilte file from my old "default" profile to my "new" profile, and still no bookmarks. rechecking the new profile, there's a file of the same size as places.squilte named places.squilte.corrupt as well as places.squilte. Where is the "html" file that the "import" tool says you're supposed to use? I can't find anything that's html that looks like bookmarks.

Firefox automatically creates a compressed .jsonlz4 in the bookmarkbackups folder when necessary (i.e. the hash value has changed).

Did you remove all other places files (sqlite-wal and sqlite-shm) when you copied places.sqlite from the previous profile?

Can copy the bookmarkbackups folder with the JSON backups as well.

• Bookmarks > Show All Bookmarks > Import & Backup

• https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them

I tried to use the jsonlz4 file but when i try to, i get an "file type unsupported" message, which is why i've been trying alternate methods. i don't see any sqlite-shm or wal files. i just copied the bookmarkbackups folder contents into the new profile and there are no booksmarks and FF opens on the Mozilla home page, but freezes again upon trying to go to another website (I tried both google and wikipedia).

i read the restore article and none of that works.

Do you have the same Firefox version that created these compressed .jsonlz4 backups?

Older Firefox versions only support the uncompressed .json format.

You can find the full version of the current current Firefox release (38.0.5) in all languages and all operating systems here:

• https://www.mozilla.org/en-US/firefox/all/

i went back into the new profile and deleted all the contents of the bookmarkbackups folder and the places.sqlite file. there was another places.sqlite.corrupt file there, despite me having deleted it minutes earlier. i restarted FF and I was able to go to google.com (no bookmarks of course). i was then able to go to wiki. so it looks to me like there's a problem with the places.sqlite file that causes FF to freeze.

i upgraded with every new version and FF started to crash almost daily, without remembering my sessions. I installed 38 and it had the same problem as my old 28 (freezing upon opening). i've been trying all these fixes on 28.

i just spotted a bunch of these in the default profile: contents-prefs.sqlite -(number, up to 9).corrupt ... CORRUPT file ... 288 kb

something is really wrong. last week, i copied my bookmarks to another computer. so i moved my default folder with the "corrupt" files out of the firefox folder, and copied ALL of the profile folders and files from the computer where FF works, thinking that somehow the corrupt files in the default folder are leaking out to corrupt the new profile. so, my only profile in the firefox folder is the one that works on my other computer. FF tries to open my home page (Wiki) and freezes -- just like it started doing yesterday. if this profile works on one computer (I used it earflier today), why isn't it working on this one?

this just keeps getting worse. i created a new profile and moved everything from the working profile on the second computer into the folder, and when i try to start FF now, I get "profile can't be loaded. it may be missing or inaccessible." But I created a profile earlier per instructions like this and it worked -- except that it was brand new and empty.

i tried using chrome to import my bookmarks and it told me that FF was running ... but it wasn't open.

if i didn't fully answer the question or about versions, i've been running 28 since last summer. i have the exe file saved, so to reinstall, i don't download anything, just run the file. when i reinstall that version and open FF, it checks for updates to "this version". if the files don't match, i don't know why.

I have another question, related to this: Both FF and Chrome mention a bookmark HTML file. There aren't any in the profile folder, nor in the bookmarkbackup folder. so where is this file?

more bad news: i deleted the new profile and put the default back so that at least i could open FF. got the same "can't open, missing or inaccessible" message.