Improve right-click behaviour near and around images

In Chrome, right-clicking repeatedly generates both a contextmenu AND a mouseup event for subsequent clicks. E.g. a sequence of right clicks generates:
1st - mousedown, contextmenu
2nd...nth - mousedown, contextmenu, mouseup

This causes problems when clicking on images as the selection is immediately reset after being processed by the first context menu, causing the subsequent mouseup event to try and reset the cursor
selection *again*.

In addition, on OSX, right-clicking on an image at the end of a range selection will cause issues if the document window doesn't currently have focus. This is because the contextmenu event is processed while the caret is hidden, changing the window selection in unexpected ways causing the selection to collapse.