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:
Notice in the screenshot above the extra-wide spacing between words, and the extra left and right padding around numerals. It’s also what I see in your screenshots.
The problem in this case is that noto-fonts-emoji has somehow taken precedence over (has a higher preference than) noto-fonts for the space character (which is extra-wide in noto-fonts-emoji) and numerals (which have extra left and right padding in noto-fonts-emoji).