I’ve updated my Switch Scrollwheel Behavior (catchy name, huh?) plugin to work with Firefox 3. No changes were made to the plugin other than updating the manifest to specify version 3.0+ as the max.
What the plugin does is toggle the value of mousewheel.withnokey.action between zero and one to switch between scrolling one screen or one line at a time when using mouse scrolling. The quickest way to invoke it is from the context menu (right-click) on a page.