Starting on March 1st, the Webflow Designer will no longer support editing sites in older Safari 7.x and 8.x browsers. Going forward, the Webflow Designer will only be available in non-read-only mode in Safari 9.0+ and Google Chrome v44+.
Safari 9.0 was released on September 30, 2015 and is available for any OSX 10.9+ users to install (including OS X v10.9 "Mavericks", OS X v10.10 "Yosemite", and OS X v10.11 "El Capitan").
According to our internal analytics, only 0.01% of all of our Safari users are using the old Safari 7 or 8 versions inside the Designer on an OS X version that does not allow upgrading to Safari 9.0 (pre-Mavericks), so we're hoping that this does not affect you.
If it does, and you are not able to upgrade to Safari 9.0 for some reason, please let us know about your situation so we can investigate.