Fix test_search and navigation menu tabs locators

Bug https://bugzilla.mozilla.org/show_bug.cgi?id=1058467
We change the weights of search results based on popularity. That is why you see other apps in there.

and Navigation Menu locator has changed https://github.com/mozilla/fireplace/commit/f6a395cc4746c724a2d9ae493b6de82d5d83e1bd