Two vague memories here: I think most of the Firefox slowness was caused by addons (both loading them at startup and adding to page latency), and Chrome's fast startup that caught casual users' eye was from completing things in the background that Firefox did before presenting the user with a UI.

Oh yes. Addons did slow things down. I think that's why I was skeptical about speed comparisons. When I ran FF on a brand new profile, it didn't feel that much slower than Chrome.

The thing is - I was happy to sacrifice speed to get the features in the addons.