Firefox Developer Edition v59 (and earlier)
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While Inspecting elements in a page refreshing the page will cause Developer Tools to switch to the Javascript debugger tab and start debugging any Javascript loaded by the page. Returning to the Inspector tab pauses the Debugger but disables further inspection that requires any click events on page elements.
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When Inspecting and clicking on an element in the page Developer Tools switches to the Javascript debugger tab and starts debugging any Javascript that may be loaded in the page.