Now I found that pressing F1 key in Web Inspector shows the pop-up help for keyboard shortcuts. I personally assign cmd-F1 to rotate windows ("Move focus to next window in application" in the OS's Keyboard preferences pane), but Web Inspector now prevents it working by taking F1 key press (and also cmd-F1) before Mac OS processes it. The keyboard shortcut for the popup help should be customizable, or at least disablable.
Closing as invalid, as this bug pertains to the old inspector UI and/or its tests.
Please file a new bug (https://www.webkit.org/new-inspector-bug) if the bug/feature/issue is still relevant to WebKit trunk.