Tell non-Firefox browsers to ignore Firefox-specific @import

Author: fregante

webext-base.css

@@ -5,7 +5,7 @@
 /* Chrome only: -webkit-hyphens */
 /* Safari only: _::-webkit-full-page-media */
 
-@import 'chrome://global/skin/in-content/common.css'; /* Firefox-only */
+@import 'chrome://global/skin/in-content/common.css' (min--moz-device-pixel-ratio:0); /* Firefox-only */
 
 :root {
 	--background-color-for-chrome: #292a2d;