You can now jump to a CSS custom property's definition from within the var() function in style rules.
On clicking the arrow here:
You get jumped to where it's defined, and it's briefly highlighted.
The events tooltip in the Inspector now shows a badge besides custom events, making it easier to differentiate them from built-in events.
I think it's the "User-defined" badges I circled:
Developer Edition? What exactly are you getting in that that you aren't getting in the regular/stable release? I tried FF.D.E. once but I found it indistinguishable from the main release. ๐ค
New features to beta test.
Features of the browser or features of the web platform?
Yes.