I have repeatedly finding myself turning to the otherwise unused Windows box on my desktop for filling in online forms. The primary reason has been the Tab behaviour in Web forms: on Windows, you can tab between text fields, menus, radio buttons, et al; on Safari/Firefox on Mac, you skip the menus entirely and have to reach for the mouse and click. And this contextual switch is costly. Now apparently this is "fixed" by enabling System Preferences > Keyboard & Mouse > Full keyboard access: "In windows and dialogs, press Tab to move the keyboard focus between: "Text boxes and lists only." Mea culpa.
I thought I'd clicked that long ago to no effect and a double-check finds that I was right. Despite the label "...and lists," it's only when you select "All controls" that tabbing to menus actually works in web forms.