> E: I forgot about the mobile Opera ports, that also tracks - I'd love to read about the engineering that went into them!

Can't really meaningfully expand on that, most of that happened before I joined in 2004, but I can tell you that the fact that Opera was extremely memory efficient made Opera Mini (250M monthly uniques, 150k web page transcodes/s) economically possible starting 2005.

We needed to keep the browser/window state around for each user until they clicked the next link. If we threw it out, any javascript state would be lost.