It may be the most used single browser version, but I'd put in the 25±10% range of visitors so it is not used by a majority of users. That said, it couldn't be

It may be the most used single browser version, but I'd put in the 25±10% range of visitors so it is not used by a majority of users. That said, it couldn't be used on a general purpose web site without at least some fallbacks.