--- a/browser/components/nsBrowserContentHandler.js
+++ b/browser/components/nsBrowserContentHandler.js
@@ -641,17 +641,17 @@ nsBrowserContentHandler.prototype = {
   validate: function bch_validate(cmdLine) {
     // Other handlers may use osint so only handle the osint flag if the url
     // flag is also present and the command line is valid.
     var osintFlagIdx = cmdLine.findFlag("osint", false);
     var urlFlagIdx = cmdLine.findFlag("url", false);
     if (urlFlagIdx > -1 && (osintFlagIdx > -1 ||
         cmdLine.state == nsICommandLine.STATE_REMOTE_EXPLICIT)) {
       var urlParam = cmdLine.getArgument(urlFlagIdx + 1);
-      if (cmdLine.length != urlFlagIdx + 2 || /firefoxurl:/.test(urlParam))
+      if (cmdLine.length != urlFlagIdx + 2 || /firefoxurl:/i.test(urlParam))
         throw NS_ERROR_ABORT;
       var isDefault = false;
       try {
         var url = Services.urlFormatter.formatURLPref("app.support.baseURL") +
                   "win10-default-browser";
         if (urlParam == url) {
           isDefault = ShellService.isDefaultBrowser(false, false);
         }