It is amazing how chaos can be harnessed into high-speed progress through ruthless CR management. Testing Web applications are exposed to millions of users who have a short attention span. If they don't like the application or it does not perform as expected, they are only one click away from the competition. Web apps should be tested against the same criteria as any other software. But a few aspects stand out as particularly important.
Usability is one of the most critical ones.
Next comes security. An e-commerce venture can be killed overnight if users get spooked by a security leak. Next on the list is browser compatibility. You should specify the oldest browser versions for which the site has to work and test the application against applicable versions of the dominant browsers. New releases should be tested on a mirror site identical to the live site.