Does this still happen if you close the sidebar in all windows and then close all but one main window and next Quit Firefox to clean up session data?

Yes, as stated in question... No Windows or tabs are open with bookmarks active. Began happening after last FF update.

I have closed out everything; all tabs and windows closed; cleared all history & data... and restarted computer several times. Nothing changes. Any help will be appreciated.

The sidebar opened state is inherited from the parent window or from the last session.

Try deleting the xulstore.json file in your profile folder when Firefox is not running.

Unfamiliar with file significance. Can you clarify which .xulstore.json file to remove? Currently, under profiles — xulstore.json — is present under two profile folders as follows:

2021: .default NOT Present 2022: .default-release-1 Present Current: .default-release Present

Can older profile folders be deleted — leaving only the Current profile folder? Thank you for your time and help.

Can older profile folders be deleted — leaving only the Current profile folder? Thank you for your time and help.

Yes, it can be deleted, not directly, but from the about:profiles page.

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

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Note that Firefox uses two locations in the hidden "AppData" location for the Firefox profile folder. One location in "AppData\Roaming" for personal data like bookmarks and logins and another location in "AppData\Local" for temporary files like the disk cache. So best is to use about:profiles to remove a profile and its files.

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

Primary location used for the main profile that keeps your personal data (Root Directory on about:profiles).

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>

Secondary location used for the disk cache and other temporary files (Local Directory on about:profiles).

• C:\Users\<user>\AppData\Local\Mozilla\Firefox\Profiles\<profile>

To all who have contributor to this thread, I thank you...

Please note… To the novice user — the information shared lacked clarity. The more I looked into the shared information, the more confused I became, until I didn’t.

Direction was given, of where I might look — however, a foreign language to the novice. Hours later (12+), it became clearer of how things are stored, what said files were, and how they might affect operations when deleted. When deleting anything in the inner workings of tech — the fear is real — WHAT might I lose?

The Solution: Deletion of the xulstore.json File (Thank you zeroknight…)

What I did not understand — was the purpose & content of this file, again, bringing up the fear of the unknown — WHAT might I lose?

FINALLY — I came to understand just WHAT the xulstore.json file even is: https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data 'A file that — “Stores the size and position of the main Firefox window and Library window, selected columns in the Library window, and expanded folders in the Bookmarks Sidebar and History Sidebar.” — Which in itself, is a bit vague, to the novice.

Looking further, to better understand this foreign language — finding that the file, once deleted — will recreate itself, in proper form.

In the end… Time ‘lost,’ though knowledge gained. Unnecessary files removed, issue resolved. Albeit an area of study I wish not to pursue — one of great benefit to understand.

Although queries may not seem complicated to the experienced — it is daunting to the novice… like asking a carpenter to remove a spleen.