Ever since Firefox 3 came out, it has been the lead browser in the whole history of the Internet. (Well, Internet Explorer is still the most well-known) 1. I have used Opera and no, it is not the fastest web browser. It loads images slow, and it has that weird Japanese flag (the white box with the red circle) before fully loading up the image. I hate that. It doesn't use that little memory. Since FF3 came out, the memory usage has decreased by a whole lot. Firefox has way more features, with the additional add-ons which will definitely make it the best browser out there. 2. Firefox uses less memory. It is also faster. 3. Opera isn't as well-known as Firefox, so that may be the reason why they don't use it. Also because Firefox IS the ultimate browser, not Opera. (No offense.) 4. Uh, sorry. I don't understand the question. I'm only 13 5. No comprendooo. Even though all of the questions I answered (3/5; :P) seem to be siding with Firefox, which was the point, I am speaking as a unbiased average Internet surfer.