no experience using firefox, IE, you can zoom font

in IE:

Click "View" from the menu bar, select Text Size, select.

Another way, change the resolution of your screen, for lower resolution, the font will be bigger. When view pic, you can set the resolution back.

Win XP, you do have the way to add the MSPY (微軟漢語拚音）， just google: how to add MSPY