Use COM standard interface instead of IHTMLDocument2 specific interface (ref gh-6).
Extrace extension check as a function (ref gh-6).
Add SPI I/F note.
Add HTML support but callback should be called (ref gh-6).
Exclude .mht as target (ref gh-6).
Add callback support (close gh-6).
Adjust trace logs.
Enable to configure initial size (close gh-2).
Though incomplete, try to hide scrollbars generally.