Do I need to download USPTO software onto my computer to use EFS-Web?

No. EFS-Web is a web-based tool. All you require is Internet access of at least 56 Kbps and a standard operating system that is compatible with EFS-Web.  You must have Adobe Acrobat Reader 7.0.8 or 7.0.9 ONLY to use the latest version of the fillable forms.

>> Download free Adobe Acrobat Reader 7+

USPTO FAQ - Questions and Answers (24FEB2007)