--- a/browser/devtools/webide/modules/simulator-process.js
+++ b/browser/devtools/webide/modules/simulator-process.js
@@ -62,18 +62,23 @@ SimulatorProcess.prototype = {
 
         Subprocess.call({
           command: "/usr/bin/osascript",
           arguments: ["-e", 'tell application "' + path + '" to activate'],
         });
       }
     });
 
-    this.on("stdout", (e, data) => this.log(e, data.trim()));
-    this.on("stderr", (e, data) => this.log(e, data.trim()));
+    let logHandler = (e, data) => this.log(e, data.trim());
+    this.on("stdout", logHandler);
+    this.on("stderr", logHandler);
+    this.once("exit", () => {
+      this.off("stdout", logHandler);
+      this.off("stderr", logHandler);
+    });
 
     let environment;
     if (OS.indexOf("linux") > -1) {
       environment = ["TMPDIR=" + Services.dirsvc.get("TmpD", Ci.nsIFile).path];
       ["DISPLAY", "XAUTHORITY"].forEach(key => {
         if (key in Environment) {
           environment.push(key + "=" + Environment[key]);
         }