Très utile pour du test.

« Font­Friend is a book­marklet for typo­graph­i­cally obsessed web design­ers. It enables rapid check­ing of fonts and font styles directly in the browser with­out edit­ing code and refresh­ing pages, mak­ing it the ideal com­pan­ion for cre­at­ing CSS font stacks.. Drag-and-drop font pre­view­ing in the browser, in any doc­u­ment you’re cur­rently viewing.»