Hi, please give this a try : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 61.0.0 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

You can check for problems with the sessionstore.jsonlz4 file in the Firefox profile folder that stores session data.

• delete sessionstore.jsonlz4 and sessionstore.js

When sessionstore.jsonlz4 is deleted you lose pinned tabs and open tabs and you will have to recreate them, so if necessary make a note or bookmark them.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

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

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

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

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

Might be interested in this once the problem is fixed : https://addons.mozilla.org/firefox/addon/multi-account-containers/

In Safe Mode it works OK, but it has 1 row of tabs. I have to add I am using multirow tabs.

I have discovered the general FF setting: Restore previous relation, is doing what I need (restores all previous tabs in the right sequence at FF startup). The subsequent Tab Session Manager feature "Restore previous session at startup" rearranges the tabs completely.

My solution for now is: I will be using the general FF setting to reopen my tabs; I will swith off the Tab Session Manager feature "Restore previous session at startup". I would use this feature only in case of emergency.

I believe there is a bug in Tab Session Manager; I hope somebody corrects this in a reasonable future.

Mila_s said

In Safe Mode it works OK, but it has 1 row of tabs. I have to add I am using multirow tabs.

Hi Mila_s, I noticed that problem trying to drag tabs along the tab bar with custom style rules that wrap the tab bar to multiple rows. I don't know of a solution.

If you find that to be an important drawback, perhaps ask over here whether anyone knows a solution for that:

https://www.reddit.com/r/FirefoxCSS/

Done, thanks.