Just like how firefox/gecko had terrible image scaling, so does webkitgtk https://bugzilla.mozilla.org/show_bug.cgi?id=486918 https://bug486918.bugzilla.mozilla.org/attachment.cgi?id=428179 QtWebKit 4.6.3 appears uses nearest neighbour, while WebKitGtk uses smooth bilinear. Smooth bilinear results in subpar image quality, therefore I suggest that webkitgtk switches to lanczos which firefox and chrome and use.
*** This bug has been marked as a duplicate of bug 50703 ***