Bug 1377284 - Enable titlebar vibrancy on macOS. r=dao

MozReview-Commit-ID: Ck9om7oS4wO

--HG--
extra : rebase_source : 31ceea6898da0107dd8f83d7a4197be7a5c1b0ab

browser/themes/osx/browser.css

@@ -1571,8 +1571,7 @@ toolbarbutton.chevron > .toolbarbutton-menu-dropmarker {
 
 %ifdef MOZ_PHOTON_THEME
 :root:-moz-any([inFullscreen], [tabsintitlebar]) #TabsToolbar:not(:-moz-lwtheme) {
-  -moz-appearance: none;
-  background-color: #232323;
+  -moz-appearance: -moz-mac-vibrancy-dark;
   color: hsl(240, 9%, 98%);
   text-shadow: none;
 }