Those are fields used by the language switcher to correlate pages across
different languages, even if they have different names/paths/titles.
They are generated with the prepare_for_translation.py script.
- mark all code blocks with ```
- unify empty lines between sections
- adjust list syntax (no space before dash)
- adjust headers to use Atx-style syntax
- remove trailing spaces
* Remove notes about pre-Firefox Quantum versions, as these are *long*
outdated
* Be clearer about U2F being deprecated and how that affects Firefox
support
