Alex RussellThis tool from Firefox DevRel is *awesome*, and if you care about how much progress the web platform delivers *please* go rank your interests:
Oblomov@slightlyoff Oh nice, it has XLST 3, JPEG XL, MathML and a number of much-need SVG features in it. Straight to the top baybee!
Pity there isn't BRING BACK RSS, COWARDS or XHTML2 support in the list though.