Intl.PluralRules: Update Firefox compat note (#5105)
Intl.PluralRules: Update Firefox compat note (#5105)

* Intl.PluralRules: Update Firefox compat note

Tomorrow’s Firefox 58 nightly will support `Intl.PluralRules` by default!

https://bugzilla.mozilla.org/show_bug.cgi?id=1403318#c18

* Add comment about hardcoding plurals

sonyarianto/WebFundamentals,samdutton/WebFundamentals,samdutton/WebFundamentals,lucab85/WebFundamentals,sonyarianto/WebFundamentals,myakura/WebFundamentals,google/WebFundamentals,agektmr/WebFundamentals,lucab85/WebFundamentals,myakura/WebFundamentals,myakura/WebFundamentals,lucab85/WebFundamentals,ebidel/WebFundamentals,google/WebFundamentals,ebidel/WebFundamentals,myakura/WebFundamentals,samdutton/WebFundamentals,ebidel/WebFundamentals,ebidel/WebFundamentals,google/WebFundamentals,agektmr/WebFundamentals,sonyarianto/WebFundamentals,samdutton/WebFundamentals,agektmr/WebFundamentals,lucab85/WebFundamentals,sonyarianto/WebFundamentals,agektmr/WebFundamentals,google/WebFundamentals