You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.

Type about:support<enter> in the address bar.

Under the page logo on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show Folder. This will open your file browser to the current Firefox profile. Now Close Firefox.

Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder

Linux: Under the page logo on the left side, you will see Application Basics. Under this find Profile Directory. To its right press the button Open Directory.

Locate the above file. Then rename or delete it. Restart Firefox.

Don't delete the files if you need to rescue any data from them, just move them out of the profile folder to some location where Firefox doesn't look for them. You can try to read out their contents using this tool: https://www.jeffersonscher.com/res/scrounger.html

i actually found the file in "sessionstore-backups" folder named "previous.jsonlz4" and realized it was my last session based on the date and time in the file info (when i last shut off my computer when firefox crashed).

i then copy & pasted that file into the main/master folder named "jwlxf24d.default". i then deleted the file named "sessionstore.jsonlz4" in that main folder, and renamed the copy & pasted file to the same one i just deleted: "sessionstore.jsonlz4".

this was the only file i needed to delete in order for my old tabs to reload.

so i then restarted firefox, and all of my old tabs loaded! psyched! thanks so much.

Glad to help. Safe Surfing.