This morning I’ve had access to a GitHub project using Internet Explorer and appeared a notification bar on the top of the page to inform that “GitHub no longer supports Internet Explorer” and suggesting to use Microsoft Edge, Google Chrome or Firefox.
You can find the list of supported browser in the following link:
https://help.github.com/en/articles/supported-browsers
Reading the supported browsers page we can find that support is offered also to Safari and that it could be limited only to the latest version of Firefox.