Created attachment 436060 [details]
If there is an inline element boundary between two elements which use the same font, but differ only in their font-feature-settings, the contextual shaping across the inline element boundary will be broken. It isn't broken in Chrome.
See attached HTML file. Unfortunately, I don't think I have the rights to post the specific font used in this example, but any font which has both contextual shaping and font features should display the bug.
Created attachment 436061 [details]
See also: https://bugzilla.mozilla.org/show_bug.cgi?id=1726891