Firefox 2.0 and Firefox 1.xx habits
With Firefox 1.x, I was used to pasting new URL in a window to open links, and I appreciated that most of new windows became new tabs (useful for gmail). On the default edgy firefox configuration, this is not the case anymore. So I changed these in the config:
user_pref("middlemouse.contentLoadURL", true);
user_pref("browser.link.open_newwindow", 3);