That's strange, I've never seen that happen. Are you using just the built-in feature ("Restore Previous Session") or a session-related add-on?

I do have Restore Previous Session turning on which I want, I just don't want it to join them all together every time. I aso have Bitwarden, Ublock Origin, Reddit Enhancement Suite, Keepa, and Vipre URL Filtering. However, none of those should affect this. It's the first time I've seen it happen as well. I am on a business network so there are group policies in effect, but none for Firefox. I have one policy active in Firefox which is for the aforementioned Vipre. Let me know if you need more info.

Tabs from other windows shouldn't move to one window when you start Firefox. When this happens then it is possible that an extension is causing the corruption of sessionstore.jsonlz4 or there is something that prevents opening new windows leading to all tabs opening in one window.

You can use this tool to check sessionstore.jsonlz4 and possibly the files in the sessionstore-backups folder to see if there is a problem with the files or something else is wrong.

• https://www.jeffersonscher.com/res/scrounger.html

I loaded the file in scrounger and to be honest I don't know what I'm looking for.

The tool should report the tabs for each individual window, so if you see more than one window with tabs then there isn't a problem with the file.

Boot the computer in Windows Safe Mode with network support to see if that has effect.

• https://www.bleepingcomputer.com/tuto.../how-to-start-windows-in-safe-mode/
• https://www.digitalcitizen.life/4-ways-boot-safe-mode-windows-10/

I see. Yes the app shows more than one window open. I will reboot and check it out.

OK, so I just rebooted and opened Firefox. The two windows opened and then one closed and all the tabs show over to the one window.

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or userChrome.css is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

OK so here's what I tried:

Troubleshooting mode - problem doesn't replicate - two windows opened. Selected Default Theme (This was not changed I installed Firefox two days ago) Disabled uBlock - reboot problem persists Pulled tabs back out to create two windows Troubleshooting mode - problem doesn't replicate - two windows opened. Disabled Reddit Enhancement Suite - reboot problem persists Pulled tabs back out to create two windows Troubleshooting mode - problem doesn't replicate - two windows opened. Disabled Keepa - reboot problem persists Pulled tabs back out to create two windows Troubleshooting mode - problem doesn't replicate - two windows opened. Disabled Bitwarden - reboot problem persists Pulled tabs back out to create two windows

Only thing left is Vipre URL Filtering which is controlled by my organization. I'm an IT admin, but don't know which policy so I will have to see how I can disable it. I am not sure if this is the issue or not, but that's the only thing left unless you have more suggestions.

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

I will test this today and report back.