Created attachment 40538 [details]
Example showing weird editing and selection behavior if ligatures are rendered
If the new CSS text-rendering property is set to "geometricPrecision" and ligatures are rendered, it is not possible to edit or select single characters/glyhps.
Created attachment 41749 [details]
Core Text part of the patch, with test
Created attachment 42142 [details]
Patch with test
Fixed in <http://trac.webkit.org/projects/webkit/changeset/50301>.