do a global replace

lib/single-file/modules/css-fonts-minifier.js

@@ -330,7 +330,7 @@ this.singlefile.lib.modules.fontsMinifier = this.singlefile.lib.modules.fontsMin
 		} else {
 			string = string.replace(REGEXP_DOUBLE_QUOTES_STRING, "$1");
 		}
-		return string.trim().replace(/\\+ +/, " ");
+		return string.trim().replace(/\\+ +/gi, " ");
 	}
 
 	function getFontWeight(weight) {