My firefox sometimes open tabs as it was before but sometimes it opens new session or session I had about month ago. That session even have my month back history,but not actual. Sync have no affect at all
Are you using more than one Firefox program or version? Are you using more than one profile?
You may have corrupt sessionstore [v56] sessionstore.jsonlz4 file(s). Delete all sessionstore* files and the sessionstore-backups folder.
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
Type about:support<enter> in the address box.
Under Troubleshooting Information on the left side, you will see Application Basics. Under this find Profile Folder. To its right press the button Show or Open 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.