Adding image of my "favorite" failure. Firefox encountered a problem restoring a blank session.

Do you have any add-ons? When is the last time you scaned your computer for virus and malware? Two things you can try is;

First, go to https://www.mozilla.org  and

download a full version of Firefox. DO NOT UPDATE! Get the install.

Second, Reset Firefox to its defaults. This will remove almost everything

from the browser, so backup EVERYTHING!

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. 

Note: This will cause you to lose any Extensions and some Preferences.

• Open websites will not be saved in Firefox versions lower than 25.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thank you.

So the answer is "dunno what's messed up but throwing away everything and starting over should fix it."

This isn't the first time I've seen Firefox mess up *exactly* like this. It seems to me a better solution would be for the developers to fix whatever they missed/broke.

But .. whatever .. I'm running Windows, and remember the bad old days so wiping out and starting over was the norm. Yeah, it is a bit blast-from-the-past but at least I remember the tune.

So, "back up everything" means WHAT in the Firefox context?

I don't mind losing cached content. I probably don't need or use all the extensions I have laying around. And only the Gods know how many cookies I have which I don't need.

Is there a useful way backup to my password database? If I copy the file can I move it back into place and still use it? Of is pen-and-paper the backup media?

I suppose I can write down the extensions which are important to me. Is there a was to back up their settings or is this also a pen-and-paper backup?

I can probably come up with a list of 100 or so cookies which are important to me. I usually miss some when I do this. But is there a way to extract and import them or back up the cookie database? Pen-and-paper won't work here except to note which web sites the process is gonna scrog for me.

I really resent having to go through a week's pain downloading, re-installing, re-configuring; then visiting hundreds of sites to check/reset passwords, and marking to catch-up on the forums I regularly follow.

No, I don't think so.

Instead, I'll mark the reply Not Helpful and leave things broken. Maybe Firefox will fix it in a few months; or maybe I'll get so disgusted I'll follow the advice .. sorta .. and demote Firefox to an "also supported" browser for my products.

Makes me sorry I even bothered asking.

If you use cleanup software like CCleaner then check the settings for the Firefox application.
Also make sure that your anti-virus software doesn't mess with files in the Firefox profile folder.

• http://kb.mozillazine.org/Profile_folder_-_Firefox

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data.

Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox profile folder.

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Multiple_profile_files_created

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).

I'm going to mark that reply "Helpful" but not solved. It helped me to see what a mess the Session Restore feature is and do some testing from a known location by deleting the JSON files. So, that's helpful.

"Session restore" is (or should properly be) an "experimental feature" since it is so buggy.

The General Option "When Firefox Starts" "Open a blank page" at least prevents Firefox from randomly re-opening closed web-chat sessions, closed banking sessions, etc. So, that option avoids the bugs in Session Restore which are opening windows and/or tabs which were by-hand closed prior to closing the web browser window (session). So, I'm declaring that "progress".

But, still, Firefox, during start-up (checked: no Firefox process running beforehand), randomly produces the screen (posted above) about an error attempting the start a new session, with a blank page, and having a problem restoring the empty old session.

So, is there another option which tells Firefox skip attempting to restore the previous session when it's opening a new session to a blank page?

What I would consider optimum (since Session Restore is a lost cause) is a Firefox session to start with ONE(1) blank tab, NO(0) errors about Session Restore failing, and at the same position and size as the most-recently-closed Firefox last-session/window (for me: primary monitor, maximized)?