Ordinarily there's an accesskey (e.g. alt+shift+E in Firefox) on the "Edit" tab in Vector. The accesskey is made known to the user through a tooltip. VisualEditor eliminates this accesskey and tooltip, and adds a new "Edit source" tab without an accesskey or tooltip.
Ideally both the "Edit" and "Edit source" tab should have accesskeys and tooltips to allow quick switching between the modes for power users.