E.g., in the inspector I can see CSS rules for an element. However, I often wonder: What was this setting for? Which values do what? I would find it helpful, if a small button would appear when I hover over a property, which offers a link to the corresponding MDN documentation. Then I don't have to use a search machine. I even don't have to let go my mouse. Just a click and I get the explanation for the CSS property in a new tab, or maybe in a separate window.
Wouldn't it be good if the MDN documentation gets linked by another product? It's some kind of integration, so to say.
This small button itself could also provide some compact information in a tooltip. But for a first step just the link would be already helpful.
The same could be done in other areas of the developer tools. E.g. in the debugger, where you could link JS functions to the corresponding MDN pages. Then I could find the documentation to something like Array.reduce() more easily, when I hover over the 'reduce' (probably only during debugging).