Re: Font in checkout, my account, etc changed size...
First, you should go back through and delete that line that you added to any files that you added it to. One thing, it's not needed for you to show a favicon, and another thing is you've hard-coded an absolute path to your image which will give a warning once you get SSL installed.
Then, once you get all that done, re-do your favicon in an icon format (.ico) instead of the .png format that you have it in. Once you get that done and uploaded to your site, it will automatically be loaded for the entire site.
If your graphics software isn't capable of saving in the .ico format, you can find free icon software by doing a Google search for "icon maker freeware". If you use Photoshop, you can Google "icon photoshop plugin" and find free ones.
That's soooooo much better and easier.
Teach them to shop and they will shop today;
Teach them to Zen and they will OWN a shop tomorrow!