When talking about employees, the plural of "staff" is not staffs, but staff. The same goes for examples such as furniture, luggage, experience, medication, which are all words we noted this week in documents and on online media that have an "s" erroneously tacked on to the end of the word.
The "s" is not necessary as the singular noun forms here include the plural.
There are also other word forms too where the "s" is not needed. Eg non-countable nouns or irregular plurals where the noun takes on a different form when pluralized. Can you think of any?