We need to opt some websites into the simulated mouse event dispatch quirk when in modern compatibility mode.
<rdar://problem/49124313>
Created attachment 367241 [details] Patch
Created attachment 367244 [details] Patch
Created attachment 367294 [details] Patch
Created attachment 367296 [details] Patch
Committed r244218: <https://trac.webkit.org/changeset/244218>