Edit>Preferences>Advanced>Mouse Wheel - voila, text zoom by mouse, and choose alt, shift, or ctrl + scroll wheel or just scroll wheel.
Download OptiMoz - voila, mouse gestures.
And still open source. *g*
But none of that helps a default zoom level. Sorry that didn't work for you, paulorcrs, but that's all I know. Check the Moz site and ask about your problem and maybe ask if there's something in your prefs.js file (or similar) that can be used to change the default. It's probably going to have to be in the files because the default is the default; I doubt there's an interface-way to change it - you'd probably have to redefine what the 100% in 'zoom=100%' meant.