I have improved my Glazoom extension for Firefox 3 based on user feedback:

  1. add a pref to open all web pages (whetever the domain) using a given zoom factor (RFE from Lyang You)
  2. add a new contextual menu item to make the whole page fit precisely into the viewport so there's no horizontal scrollbar (RFE from Steve Ranta).

I am currently testing my implementation and will push it to addons.mozilla.org as soon as possible.