You may have corrupt sessionstore file(s).

Places Maintenance {web link} Allows to run Maintenance tasks on the database that drives Places, the bookmarks and history module behind Firefox.

If the above did not help,

Type about:support in the address bar and press enter.

Under the page logo on the left side you will see Application Basics. Under this find Profile Folder. To it’s right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Locate the sessionstore file(s). Then rename or delete it. Restart Firefox.

Thank you, FredMcD: I have installed Places Maintenance, but it seems to have 6 features: Check Integrity, Rebuild Indices, Expire, Check Coherence, Vacuum, and Statistics (none of which I understand/know about). Should I run/execute all of them? Should I restart FF after I run the maintenance you recommend? I have not yet tried your second suggestion (renaming the sessionstore file).

Thanks for being so responsive. GNorman

This is probably caused by a problem with closing down Firefox the last time and the sessionstore.js that got created is corrupted.

The sessionstore.js file is created from recovery.js when you close Firefox and is removed and copied to previous.js when you start Firefox.

You can backup the session files in the sessionstore-backups folder in the Firefox Profile Folder to make sure not to lose possible important session data.

previous.js (cleanBackup: copy of sessionstore.js from previous session that was loaded successfully)
recovery.js (latest version of the sessionstore written during runtime)
recovery.bak (previous version of the sessionstore written during runtime)
upgrade.js-<build_id> (backup created during an upgrade of Firefox)

You can copy a file from the sessionstore-backups folder to the main profile and rename the file to sessionstore.js to replace the current file (make a backup copy of the current sessionstore.js).

You can open such file in the Scratchpad (Firefox/Tools > Web Developer) to see if there are URL of web pages present. Click the "Pretty Print" button to format the file for readability.

• https://developer.mozilla.org/Tools/Scratchpad

GNorman said

I have installed Places Maintenance, but it seems to have 6 features

Every now and then, run all of the tests.

I ran all 6 of the Place Maintenance facilities, and restarted FF, but the same issue persists -- lots of empty tabs.

As I was pursuing your suggestions, Cor-El weighed-in with an idea that sounded very close to your 2nd suggestion: Renaming sessionstore files (he seems to suggest a back-up first, but it wasn't clear to me where, since back-up files are already in a back-up folder). I'm a bit confused:

In the Profile Folder are two files, sessionstore.bak and sessionstore.bak-[build ID], but both are dated 2014; there is also a subfolder, "sessionstore-backups", and it contains recovery, previous, and upgrade files, all of which have different dates (this subfolder does not contain any sessionstore files). You and Cor-El know far more than me ... so I'm hoping for step-by-step instructions that will help me to back-up critical files, and then guide me through which files to rename, which seems to be one of the sessionstore files now dated 2014.

I'm not a Luddite, just not well-versed in how the engine room works. I am most grateful for any help. GNorman

Older Firefox versions used sessionstore.bak as a backup for sessionstore.js that is used when you start a new session (sessionstore.js was renamed to sessionstore.bak in older Firefox versions). The sessionstore.bak file is no longer used in current releases as you can see by the old file date.

In the current release all sessionstore files used during a session are in the sessionstore-backups folder and only when Firefox is closed sessionstore.js is created and used to restore the session on startup. I wrote in my above reply some information about the files in the sessionstore-backups folder. With making a backup of the files in the sessionstore-backups folder I meant to copy them all to another folder to have a backup copy of them elsewhere.

The sessionstore.js file is created from recovery.js when you close Firefox and is removed and copied to previous.js in the sessionstore-backups folder when you start Firefox.

I suspect that something went wrong in the previous session and that either Firefox didn't close properly or something else went wrong and a corrupted or incomplete sessionstore.js file got created. I don't think that this is a problem with the history (places.sqlite) and thus Places Maintenance won't be of help. I don't know if you can still restore the tabs from that older session, so you would have to check the files in the sessionstore-backups folder like I wrote above. You can open them in a Firefox tab or in the Scratchpad (Firefox/Tools > Web Developer). The latter has a "Pretty Print" button that allows to format the file foe better readability (each of these files is one long line without any line breaks).

Thank you for your continued feedback; I now understand the difference between the files and their respective locations.

The suggestion to rename files may have worked had I known of it when the "empty" tab issue first appeared. Since I have closed and re-opened FF after the problem presented, both the "recovery" and "previous" js files are now set/dated post-problem, ie, they contain no URLs. In other words, on 8/21, I closed a FF session successfully (or so I thought); on 8/22, I opened FF with its now empty tabs, then closed it, and did so again today, 8/23. I used Scratchpad, and both the recovery and previous js files are dated 8/23 and are loaded with blank URLs; there are no files dated 8/21, when FF last remembered my tabs.

Seems like the tabs' URLs are gone -- correct? Any other place they might be found? This all happened on my desktop; I have sync turned-on, but if I try to sync from my laptop, won't it just find a bunch of empty tabs?

What's weird is that FF "knows" there are tabs -- it just doesn't remember each tab's URL.

Thanks again, to both yourself and FredMcD. Any add'l wisdom would be very much appreciated. G. Norman