They aren't, they're commenting on company general policy and making the obvious deduction from that.
It's (literally) basic logic
1. Some site flags Firefox.
2. Not all sites flag Firefox.
3. Either every site flags Firefox or individual sites flag Firefox.
4. It is not true that every site flags Firefox (obverse of 2)
C. Individual sites flag Firefox (disjunction with 3, 4)
It's (literally) basic logic
1. Some site flags Firefox. 2. Not all sites flag Firefox. 3. Either every site flags Firefox or individual sites flag Firefox. 4. It is not true that every site flags Firefox (obverse of 2) C. Individual sites flag Firefox (disjunction with 3, 4)