A new appreciation for Firefox's 'Performance' web developer tool
Then recently I had my experience with Firefox WebRender, and I realized that the Performance stuff can tell me things about how Firefox itself is performing. It's one thing to feel that WebRender made my Firefox laggy (and that perception matters), but it's another thing to be able to look at Performance's FPS report and see that it is objectively worse. It's reassuring that it's not just my perceptions, and it's also reassuring that in some way Firefox can actually see the problem (since it saw lower FPS figures).
Now that I've discovered this use of it, I'm probably going to pay more attention to Performance and play around with it more. Perhaps this will also lead to me exploring other of the developer tools.