Don't delay Firefox startup

lib/io.js

Index: lib/io.js
===================================================================
--- a/lib/io.js
+++ b/lib/io.js
@@ -65,84 +65,133 @@ let IO = exports.IO =
    * Reads strings from a file asynchronously, calls listener.process() with
    * each line read and with a null parameter once the read operation is done.
    * The callback will be called when the operation is done.
    */
   readFromFile: function(/**nsIFile|nsIURI*/ file, /**Boolean*/ decode, /**Object*/ listener, /**Function*/ callback, /**String*/ timeLineID)
   {
     try
     {
+      let processing = false;
       let buffer = "";
+      let loadEvent = null;
+      let errorEvent = null;
       let uri = file instanceof Ci.nsIFile ? Services.io.newFileURI(file) : file;
       let request = new XMLHttpRequest();
       request.mozBackgroundRequest = true;
       request.open("GET", uri.spec);
       request.responseType = "moz-chunked-text";
       request.overrideMimeType("text/plain" + (decode ? "? charset=utf-8" : ""));
 
-      request.addEventListener("progress", function(event)
+      let onProgress = function(event)
       {
         if (timeLineID)
         {
           TimeLine.asyncStart(timeLineID);
         }
 
         let data = event.target.response;
-        let index = Math.max(data.lastIndexOf("\n"), data.lastIndexOf("\r"));
+        let index = (processing ? -1 : Math.max(data.lastIndexOf("\n"), data.lastIndexOf("\r")));
         if (index >= 0)
         {
-          let oldBuffer = buffer;
-          buffer = data.substr(index + 1);
-          data = data.substr(0, index + 1);
-          let lines = data.split(/[\r\n]+/);
-          lines.pop();
-          lines[0] = oldBuffer + lines[0];
-          for (let i = 0; i < lines.length; i++)
-            listener.process(lines[i]);
+          // Protect against reentrance in case the listener processes events.
+          processing = true;
+          try
+          {
+            let oldBuffer = buffer;
+            buffer = data.substr(index + 1);
+            data = data.substr(0, index + 1);
+            let lines = data.split(/[\r\n]+/);
+            lines.pop();
+            lines[0] = oldBuffer + lines[0];
+            for (let i = 0; i < lines.length; i++)
+              listener.process(lines[i]);
+          }
+          finally
+          {
+            processing = false;
+            let e = {
+              target: {response: buffer}
+            };
+            buffer = "";
+            onProgress(e);
+
+            if (loadEvent)
+            {
+              let event = loadEvent;
+              loadEvent = null;
+              onLoad(event);
+            }
+
+            if (errorEvent)
+            {
+              let event = errorEvent;
+              errorEvent = null;
+              onError(event);
+            }
+          }
         }
         else
           buffer += data;
 
         if (timeLineID)
         {
           TimeLine.asyncEnd(timeLineID);
         }
-      }, false);
+      };
 
-      request.addEventListener("load", function(event)
+      let onLoad = function(event)
       {
+        if (processing)
+        {
+          // Still processing data, delay processing this event.
+          loadEvent = event;
+          return;
+        }
+
         if (timeLineID)
         {
           TimeLine.asyncStart(timeLineID);
         }
 
         if (buffer !== "")
           listener.process(buffer);
         listener.process(null);
 
         if (timeLineID)
         {
           TimeLine.asyncEnd(timeLineID);
           TimeLine.asyncDone(timeLineID);
         }
 
         callback(null);
-      }, false);
+      };
 
-      request.addEventListener("error", function()
+      let onError = function(event)
       {
+        if (processing)
+        {
+          // Still processing data, delay processing this event.
+          errorEvent = event;
+          return;
+        }
+
         let e = Cc["@mozilla.org/js/xpc/Exception;1"].createInstance(Ci.nsIXPCException);
         e.initialize("File read operation failed", result, null, Components.stack, file, null);
         callback(e);
 
         if (timeLineID)
         {
           TimeLine.asyncDone(timeLineID);
         }
-      }, false);
+      };
+
+      request.addEventListener("progress", onProgress, false);
+      request.addEventListener("load", onLoad, false);
+      request.addEventListener("error", onError, false);
 
       request.send(null);
     }
     catch (e)
     {
       callback(e);
     }
   },