I should say this has been an intermittent problem for quite awhile on my desktop through various versions of Firefox. Someone must have a clue?

By not updating, you mean you open a new tab or a new window and Firefox does not write the new information to recovery.js? By default, the file should update every 15 seconds if there are changes...

I know you said your preferences are the same between computers, but could you let us know if you have any non-default settings here:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste sess and pause while the list is filtered

(3) Are any preferences starting with browser.sessionstore preference bolded and "user set"? If so, which ones?

On mine, browser.sessionstore.upgradeBackup.latestBuildID and browser.sessionstore.upgradeBackup.maxUpgradeBackups are bolded; the first may be modified by Firefox, the second I might have modified, I don't remember, the current default value is only 3 and mine is set to 10.

Are there any "extra" files in the sessionstore-backups folder? To check on that:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show Folder" button.

In the window that launches, scroll down and double-click into the sessionstore-backups folder. You can expect to find:

• recovery.js: the windows and tabs in your currently live Firefox session
• recovery.bak: a backup copy of recovery.js
• previous.js: the windows and tabs in your last Firefox session
• upgrade.js-build_id: the windows and tabs in the Firefox session that was live at the time of your last update

Note: By default, Windows hides the .js extension. To ensure that you are looking at the files I mentioned, you may want to turn off that feature. This article has the steps: http://windows.microsoft.com/en-us/windows/show-hide-file-name-extensions

Is there anything extra or unexpected?

Correct, the recovery.js file rewrites itself (i.e. updates) for a few minutes at most after Firefox is started and then stops. It won't update again until Firefox is restarted.

No idea on this one, but like you this is User Set: browser.sessionstore.upgradeBackup.latestBuildID: 20160210153822 But it is also listed as User Set on my laptop.

No extra files, just: recovery.js recovery.bak Sometimes I have an upgrade.js file but not always/regularly. I haven't seen a previous.js file much recently and don't have one now. But I have had one sometimes in the past.

Hmm, some other process might be locking the file, but I don't know how to check for that.

Could you tell me a couple settings from the Options page:

(1) General panel

• Startup - Is Firefox set to start up with your previous session windows and tabs, or your home page?

(2) Privacy panel

• "Remember my browsing and download history" is turned on?
• If "Clear history when Firefox closes" is turned on, click Settings, and check whether "Browsing & Download History" is selected for clearance

Sometimes inexplicable breakage is due to problems in the program folder. To address that we generally suggest:

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. Do NOT uninstall Firefox, that's not needed.

(A) Download a fresh installer for Firefox 44.0.2 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.) Note: For broadest compatibility, choose the 32-bit version.

(B) Exit out of Firefox (if applicable).

(C) Rename the program folder as follows:

(32-bit Firefox on 64-bit Windows)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(Other versions)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.

Does a cleanly reinstalled Firefox update session history?

Note: Some plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

Previous windows and tabs. Remember history.

I'll try a clean install. Will Extensions copy over or will I have to redo them?

The clean reinstall using the steps I posted only affects the program folder. Do not rename or remove any other folders. Your extensions should not be affected, nor any settings.

Are you using "Clear history when Firefox closes" to clear the browsing history?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

I'm not using clear history when Firefox closes.

Clean re-install seems to have done it, thanks!