More regexp fixes for mozilla5 compatibility.

im/content/joinchat.js

@@ -78,7 +78,7 @@ var joinChat = {
 
       let label = document.createElement("label");
       let text = field.label;
-      let match = /_(.)/(text);
+      let match = /_(.)/.exec(text);
       if (match) {
         label.setAttribute("accesskey", match[1]);
         text = text.replace(/_/, "");

purple/purplexpcom/src/imCommands.js

@@ -216,7 +216,7 @@ CommandsService.prototype = {
 
     let matchResult;
     if (aMessage[0] != "/" ||
-        !(matchResult = /^\/([a-z]+)(?: |$)([\s\S]*)/(aMessage)))
+        !(matchResult = /^\/([a-z]+)(?: |$)([\s\S]*)/.exec(aMessage)))
       return false;
 
     let [, name, args] = matchResult;