Right now it just changes color. There is a small regression from features from the web extension, where the label changed from "Gecko Profiler (on)" and "Gecko Profiler (off)". This label should be updated in devtools/startup/ProfilerMenuButton.jsm by directly modifying the attribute. The problem is that the .jsm file doesn't directly have access to localization dependencies. I'm not sure what's the best course to localize that label, hence this bug, which can investigate it.

$("#profiler-button").setAttribute("tooltiptext", "The profiler is running")

Thanks for the bug! The title can indeed be important for screen reader users.
I'd like to add that we should also change the shape of the icon (for example with a shadow or something ?) when it's on, this is for folks that can actually see but don't see colors right.

Idea:

• Stopped should have the hand pointing up,
• Running could have the hand elsewhere, and maybe some "speed lines" to infer movement, or filling the space between "noon" and the hand position.

I'm guessing animating it would be too distracting and resource-wasting.

The icon itself now changes, and the tooltip (localized) also changes, so I believe this is now fixed.