It actually takes about the same amt of time to LOAD the program itself. Here's the difference with Opera vs. Firefox.
Firefox makes you wait until everything is loaded before you can click stuff/scroll down. This can be frustrating if you dont really need to see the whole page. Opera also has MUCH faster multiple image loading, and it uses less resources. So I'll be using opera for most of my browsing on the slow comp.
Dont get me wrong, Firefox is still my browser of choice (and will always be), but on 32MB RAM and 250MHz, I need the fastest i can get