Normalise regex -> regexp.

This is what JS uses and using both is confusing.

common/modules/storage.jsm

@@ -511,7 +511,7 @@ const File = Class("File", {
 
         // expand ~
         // Yuck.
-        if (!relative && RegExp("~(?:$|[/" + util.escapeRegex(File.PATH_SEP) + "])").test(path)) {
+        if (!relative && RegExp("~(?:$|[/" + util.escapeRegexp(File.PATH_SEP) + "])").test(path)) {
             // Try $HOME first, on all systems
             let home = services.get("environment").get("HOME");
 

common/modules/util.jsm

@@ -330,7 +330,7 @@ const Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference])
      * @param {string} str
      * @returns {string}
      */
-    escapeRegex: function escapeRegex(str) {
+    escapeRegexp: function escapeRegexp(str) {
         return str.replace(/([\\{}()[\].?*+])/g, "\\$1");
     },