[fixed-z-index-blend.html]
disabled:
if os == "mac": https://bugzilla.mozilla.org/show_bug.cgi?id=1552460
if os == "win": https://bugzilla.mozilla.org/show_bug.cgi?id=1552460
if os == "android": https://bugzilla.mozilla.org/show_bug.cgi?id=1559313
expected: [PASS, FAIL]