optimizeLegibility is a CSS declaration that improves the handling of kerning pairs and ligatures in the browsers that support it; it makes text easier to read by spacing the letters correctly. It makes quite a bit of difference, particularly on larger font sizes, as you can see in the screenshot below:
optimizeLegibility is a declaration that has to be enabled using text-rendering: optimizeLegibility; — if the designer hasn’t included it, the browser won’t use it (with the exception of Firefox, which already uses optimizeLegibility by default on fonts with a size of over 20px).
If you’d like optimizeLegibility to be enabled by default in Safari or Chrome, there are some simple extensions that you can use. For Safari, you can try either Paul Kehrer’s Optimize Legibility extension, Chris Morrell’s Optimize Legibility extension or Jim Ray’s Kerning extension, while John Michel has made a similar extension for Chrome. Apparently using optimizeLegibility could cause a performance hit, but I’ve noticed no problems on my machine.
Do you use any extensions or tricks to improve the legibility of websites? Share them below.