CREATE TABLE table_13301 ("Period" TEXT, "Internet Explorer" TEXT, "Firefox" TEXT, "Safari" TEXT, "Opera" TEXT, "Netscape" TEXT, "Other Mozilla" TEXT)

What percentage of users were using Netscape during the period in which 21.67% were using Firefox?
SELECT "Netscape" FROM table_13301 WHERE "Firefox" = '21.67%'
SELECT "Netscape" FROM "table_13301" WHERE "Firefox" = '21.67%'