I cannot open zip folder in Firefox Windows 7

[Skirball]

So just download the file, save it to your computer, and open it outside the browser (e.g. double click it in windows explorer)

[Vetteran]

. . . and be sure that the source is trustworthy!

[Tomsm]

or you can use the online services,
or save the zip on your computer and open with your archiver