Earlier quoted context omitted.
Installing extensions can dramatically slow down browsers. I wonder if the lack of extensions is responsible for the quickness users experience with a fresh install.
That's my biggest reason for switching from AdBlock+ to Privoxy + https://github.com/skroll/privoxy-adblock . Same blocking rules but uses a ton less memory, since each tab isn't running all of AB+ .
Of course, if you don't want that, you're sweet.