When you type in the search field on the new tab page, the address bar switches to search mode using your current engine. When I type "/foo", my address bar enteres Google search mode, and when I press enter, I get a Google search for "/foo". Does it not do that for you?
Bug 1754546 Comment 8 Edit History
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When you type in the search field on the new tab page, the address bar switches to search mode using your current engine. When I type "/foo", my address bar enters Google search mode, and when I press enter, I get a Google search for "/foo". Does it not do that for you?