[1] [2] [3] [4] [5] I obviously tried other fonts besides Noto Sans (Dejavu, Cantarell). I also tried to use fc-cache --really-force The font of the numbers and space is also very strange

Do you happen to have noto-fonts-emoji installed on your system? If so, temporarily uninstall noto-fonts-emoji, reboot (or log out/in), and check Firefox again. The problem reported here seems similar to yours: [image] r/archlinux - Issues about font: has space between words Bis jetzt …