Seems to work. I didn't check this simple solution myself. I had to to do it. But now I will keep it in mind. Thank you for your very quick help.
Another question if I'm allowed. Mostly it needs up to an hour to show the stats of my local bookmarks (about 10.000). Sometimes it's shown after some minutes. The stats of my online bookmarks are mostly shown after seconds. Is this normal behaviour?

Tabs of Eversync (e.g. Bookmarks) are shown for less than a second when pressing F5.
Firefox is 70.0.1 (64-Bit)