We've discussed text size issues a few times recently -- for instance here, here and here.

Ctrl and + does work for me. So does holding down Ctrl and turning the scroll wheel on my mouse. (No scroll wheel on your mouse?! ) On every browser that I've tried, there's a way to change font size from the menus. In Firefox it's done through View > Zoom. That same menu shows Ctrl and + as the keyboard shortcut.

If the Ctrl-and-+ key combination didn't work for me in the browser I was using, I think I'd want to (a.) try it with a different browser and (b.) see if it worked any differently at other websites.