The font event API is out in Chrome and coming in Firefox 36 but you can use it now with this polyfill
Jonathan Suh writes:
Web fonts are great and make the web a more beautiful space; however, loading them can be slow, which results in an unwanted side effect: FOIT (Flash of Invisible Text). I’ve experienced FOIT on my website, particular on mobile connections, but with the help of some homework and fantastic resources, plus some JavaScript and CSS, I managed to fix it.
Also see http://caniuse.com/#feat=font-loading
Read the full article Jonathan Suh