List of all tabs (arrow down) shows also closed tabs and restores them
After an upgrade to version 74.0 on Linux Mint the "List of all tabs" (arrow down) shows also already closed tabs and therefore restores them after reopening the FF.
Try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.
You can find the full version of the current Firefox release (74.0) in all languages and all operating systems here:
The problem was an error in my userChrome.css Thanks.