Bug 1510565 - Fix download panel button color. r=paolo

Differential Revision: https://phabricator.services.mozilla.com/D15814

--HG--
extra : moz-landing-system : lando

browser/themes/shared/downloads/downloads.inc.css

@@ -176,7 +176,7 @@
   border: none;
   background: transparent;
   padding: 0;
-  color: inherit;
+  color: inherit !important /* !important overrides button.css on Mac and Linux */;
 }
 
 .downloadButton > .button-box > .button-icon {