My fonts have shrunk!

[Bananadude]

On numerous websites, my fonts have shrunk, and in some cases it's barely readable! Have I inadvertently changed a setting or something!!? Surely this can be fixed with a simple setting??

 

[Killa_ken]

Hold control and move your scroll wheel up and down

 

[Tony Williams]

For FF, hold ctrl and fiddle with *** scroll wheel and for IE do *** same.