diff --git a/components/CommandLine.js b/components/CommandLine.js
new file mode 100644
index 0000000..141c097
--- /dev/null
+++ b/components/CommandLine.js
@@ -0,0 +1,88 @@
+const CATEGORY = 'c-mozrepl';
+const CONTRACT_ID = '@mozilla.org/commandlinehandler/general-startup;1?type=repl';
+
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cr = Components.results;
+const CLASS_ID = Components.ID('{f62cbe68-ee70-4264-8586-66df185244f5}');
+
+const Handler = {
+    QueryInterface: function(iid) {
+        if(iid.equals(Ci.nsICommandLineHandler) ||
+           iid.equals(Ci.nsIFactory) ||
+           iid.equals(Ci.nsISupports))
+            return this;
+
+        throw Cr.NS_ERROR_NO_INTERFACE;
+    },
+
+    handle: function(cmdLine) {
+        var uri;
+        try {
+            uri = cmdLine.handleFlagWithParam('repl', false);
+        } catch (e) {
+        }
+
+        if(uri || cmdLine.handleFlag('repl', false))
+            Cc['@hyperstruct.net/mozlab/mozrepl;1']
+            .getService(Ci.nsIMozRepl)
+            .start(4242);
+    },
+
+    helpInfo: '-repl              Start REPL.\n',
+
+    createInstance: function(outer, iid) {
+        if(outer != null)
+            throw Cr.NS_ERROR_NO_AGGREGATION;
+
+        return this.QueryInterface(iid);
+    },
+
+    lockFactory: function(lock) {
+        /* no-op */
+    }
+};
+
+
+const Module = {
+    QueryInterface: function(iid) {
+        if(iid.equals(Ci.nsIModule) ||
+           iid.equals(Ci.nsISupports))
+            return this;
+
+        throw Cr.NS_ERROR_NO_INTERFACE;
+    },
+
+    getClassObject: function(compMgr, cid, iid) {
+        if(cid.equals(CLASS_ID))
+            return Handler.QueryInterface(iid);
+
+        throw Cr.NS_ERROR_NOT_REGISTERED;
+    },
+
+    registerSelf: function(compMgr, fileSpec, location, type) {
+        compMgr.QueryInterface(Ci.nsIComponentRegistrar);
+        compMgr.registerFactoryLocation(CLASS_ID, 'Handler', CONTRACT_ID, fileSpec, location, type);
+
+        var catMan = Cc['@mozilla.org/categorymanager;1'].getService(Ci.nsICategoryManager);
+        catMan.addCategoryEntry('command-line-handler', CATEGORY, CONTRACT_ID, true, true);
+    },
+
+    unregisterSelf: function mod_unreg(compMgr, location, type) {
+        compMgr.QueryInterface(Ci.nsIComponentRegistrar);
+        compMgr.unregisterFactoryLocation(CLASS_ID, location);
+
+        var catMan = Cc['@mozilla.org/categorymanager;1'].getService(Ci.nsICategoryManager);
+        catMan.deleteCategoryEntry('command-line-handler', CATEGORY);
+    },
+
+    canUnload: function (compMgr) {
+        return true;
+    }
+};
+
+function NSGetModule(comMgr, fileSpec) {
+    return Module;
+}
+