Meet FontFonter, a neat online app that lets you change the font styles of your favorite websites with a simple click. Enter a website address, choose which type of fonts (serif or sans-serif or both) you want to replace and then pick a target typeface – you’ve more than 40 different fonts to choose from.
What’s nice about Font Fonter is that while previewing a website in a different font, you can go any levels deep and the pages will still render in the previously selected typeface.
This helps when sites use different styles for the home page and inner pages or when you are a search page and are navigating to a new page that could be using a completely different typeface – your font selection will be preserved during the entire session.
You need Firefox or Chrome to use Font Fonter, it simply won't work in IE and Opera. FontsLive, another font vendor, also offers a similar preview service where you can again replace the default font styles of a web page with premium web fonts.
Preview Web Pages in Google FontsThe Font Fonter app is nice but you can preview web pages in a select range of commercial web fonts. However, there’s an awesome Chrome extension as well that will let you change fonts of a web page to any of the Google Web Fonts that are completely free and can be used anywhere without restrictions.
And with the font preview extension, you can not only change the fonts of a web pages but also their size, style and other text attributes. Thank you @SwissMiss for the tip.