so achiever is a software in it self(dont need firefox, etc..). I was in your same situation w/ almost broken laptop. But i brought it for my desktop. & it only works on desktop(my stable computer) b/c i purchased it on my desktop. Buy it only on stable computer b/c they wont let you activate the product on different computer.
What achiever does is pretty shady... after you purchase the software they will give you the link to download it. its only 6 or 7mb something like that. The shady part is they are trying to save money. Unlike top score(100+ mb) which lets you download all of the software including their question database. Achiever only lets you download the software and the questions are on the servers database of Achiever company. So this way they can save a lot of money on bandwidth.
The first thing Achiever does is downloads all the text b/c as we all know text is small file size. Then any questions that requires images ie. organic chemistry or pat or math, bio, chem. It downloads images on demand so only when you come to that particular question. Then only it downloads that image. again saving bandwidth. So if you have slow internet image questions will take little longer to load. & if you lose internet connection in the middle of the pat. You will just see ABCD but no pictures. This way they wont lose money if you quit your exam in the middle or if you only want to take couple sections. etc...