An annoyance with the latest Firefox 3 Beta.The ctrl-scroll wheel (aka mousewheel) page text resize shortcut inexplicably reversed itself since the last version of Firefox I was using. That is, Ctrl-WheelDown now makes the text smaller, whereas before it made it larger.
In fairness to Mozilla, this change actually makes the behaviour more in line with guidelines and probably, if you were a brand new Firefox user, it'd be more intuitive too.
But for those of us who have grown accustomed to the old behaviour and don't want to bother retraining muscle memory, here is the secret... go to Firefox's about:config settings page (type about:config into the location bar) and find the "mousewheel.withcontrolkey.numlines" setting, and change it from positive one to negative one. That is, after the change, the relevant prefs should be:
mousewheel.withcontrolkey.action = 3
mousewheel.withcontrolkey.numlines = -1
Problem solved. More information at Mozilla bug #141476.
Update: You may also want to install the excellent NoSquint extension, also available at the official Firefox addons page. It remembers your preferred zoom levels per site. I'd also recommend setting your primary zoom method to Text Zoom only... but that's more personal preference I think.