If the fonts of all your browsers seem to be bold and/or smaller or more are large when you visit a page of WordPress or another web site in particular. Perhaps this little trick is the solution to your problems. This tutorial is only for OS Mac OS X, version 10.6 onwards.
1. Opens the Font Book application in your applications folder and look for the "Open Sans" font.
2. Find: Once you select the source, right-click and then click on "Show in Finder" or "Show in Finder" If you have the operating system in Spanish.
3. Move: This action you will show in a folder in the Finder with all sources that you have selected in the Font Book. You do not dispose of any font or change their names, as this could create conflicts in other programs, simply move them to your desktop and see how immediately your Firefox or Safari browsers change back to its original text format. So this affects Google Chrome you should refresh all your open tabs or restart the application (close and open Chrome).
2 Final result: