macOS tends to need higher resolution icons in some cases, mainly when doing hidpi. Unfortunately their icon format does not include any vector version, so we need to make sure to include some high resolution variants. Right now we get a blurry version as the system scales up our current icon.
This got fixed in r38314 for bug 7911. I now get crisp icons everywhere on macOS, even when 2x high dpi is enabled.
Tested as part of bug 7911 using client build #2545 with a 4k display and scaling turned up to max. The icon still looks crisp. Closing.