Archive for March, 2011

Cloud Printer – Print from Firefox Mobile

Recently, Google released the beginnings of a cloud-based printing system called – Google Cloud Print. The project is still in Beta, but you can install a recent version of Google Chrome on Windows and attach your local printers into the Cloud Print system (more). Google has added support for Cloud Print to few of their mobile web apps, but has not released a client application API yet. However, they did release a simple webapp demo – and where there is a demo, there are people reverse engineering it.

Cloud Printer is a restartless Firefox Mobile add-on that integrates into the Google Cloud Print system. Firefox Mobile already has code to save web pages as PDF. I took that code and send the PDF to the Google Cloud Print system.

Using the demo code and some other examples, it was fairly simple to get this to work. The current API is fairly simple and nice. I expect a few changes when the APIs become official, which should happen soon.

Note: You need to be signed into your Google Account for this to work. If you are not signed in, you’ll see a prompt and we open the Google Account login page for you.

Let me know how this works for you!

Restartless Fun

I like experimenting with restartless add-ons. This time I used a variation of the include technique to assign an image to the toolbar button and get access to a CSS file and IPC frame script. The CSS file is loaded and unloaded using nsIStyleSheetService. The IPC frame script is loaded using the global message manager. The frame script is needed because the PDF file must be generated in the content process, not the main process. You do remember that Firefox Mobile is multi-process, right?

One gotcha. Once loaded, you can’t currently unload a IPC frame script. So if you enabled/disable a restarless add-on that loads a frame script, you’ll end up with multiple instances running. Which means, when you send an IPC message, multiple listeners will respond – this is bad. I hacked around that by sending a “disable” message to my frame script when uninstalling the add-on. The “disable” message just removes the message listeners in the frame script so they won’t respond to any messages in the future. See the source code.

These restartless techniques are documented in various places, but we should start some code snippet docs on MDC too.

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Firefox Mobile Add-on – Cloud Viewer

I just put together a simple restartless add-on, Cloud Viewer, that integrates the Google Docs Viewer into Firefox Mobile. I saw a few similar add-ons on AMO for desktop Firefox, but none for Firefox Mobile. Opera and Dolphin also have add-ons integrating support for online document viewers.

The concept is pretty nice, especially for mobile devices: Open online documents in an online viewer. No need to waste time downloading the file and waste space on your device saving the file. Google’s viewer supports Powertpoint (PPT), Word (DOC, DOCX), Excel (XLS, XLSX), PDF and some non-web image formats. The viewer even uses a mobile UI when running on devices.

Restartless Fun – The Details

I wanted the add-on to be restartless because restartless add-ons rock. I also wanted the add-on to work at a deeper level than a context menu. I could have put a menu item on the context menu to open links in Google’s viewer, but that wouldn’t work on links that weren’t directly pointing to the file – think Google search results. The link Google gives you in a search result redirects you to the actual file, so a context menu item wouldn’t be the best solution. The redirection issue occurs more than you think on the web. Instead, I override an XPCOM component the controls how Firefox treats files the browser doesn’t natively handle. Normally, this component (nsIHelperAppLauncherDialog) starts a file download and will open the file using a local application.

Cloud Viewer overrides the component. I check the extension of the direct URI to the file and if supported, I ask the user if we should open the file in an online viewer. Since the add-on is restartless, I can’t use the normal method of registering JS XPCOM components. I have to manually register and unregister the component myself. This worked fine and was pretty easy. See the source code.

I really think we should be writing more restartless add-ons, especially the simple ones. Great UX and a really small download. Only 2.5KB XPI file for Cloud Viewer. The internal support for restartless add-ons will only keep getting better.

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Zippity & Test Harness Updates

A few weeks ago I posted about Zippity, a way for anyone to help collect performance data for Firefox Mobile. Data has been coming in and so has some feedback. I added some features to the Test Harness add-on to make it easier to use and collect some new types of data. Here’s a list of changes:

  • Added a proper in-content page for starting tests, and checking out previous result.
  • Added support for measuring startup time, as well as, SunSpider and V8 JS benchmarks.
  • Added basic support for desktop Firefox (thanks to Dietrich Ayala.)
  • Added a page timeout for pageload tests. Sometimes pages just get stuck – either a bug in Fennec or a mystery of the ether.
  • Added a simple goodput measure for pageload tests. We time how long it takes to download a 250KB test file from Zippity. It’s a simple metric we can use to categorize the pageload results.

All tests are preconfigured, you just need to tap the test you want to run and the add-on does the rest. Here’s a basic rundown of how each test works, so you have an idea of what to expect:

  • Pageload: Opens a new tab and starts loading a predefined list of pages. We load the list of pages 3 times and take the average.
  • Startup: Fennec will restart itself five (5) times, remembering the startup time for each restart and then taking the average. Startup time is defined as the time from launching the process to the end of loading the initial page.
  • SunSpider and V8: Each subtest of the benchmark is a web page, loaded and executed. The page reports the time needed to complete the subtest. The final result is the total of all subtests.


I also updated the Zippity server to support the new data types and added some new features:

  • Added graphs for viewing startup time, SunSpider and V8 results.
  • New mobile pages built using jQuery Mobile. Now you can install the add-on and view the graphs from your mobile device. Still needs some tweaks, but it’s a start.
  • Added the goodput measure to the graph tooltips. Will only appear for newly collected data that has the metric.

The SunSpider and V8 tests are taken from the Mozilla Talos test suite. The Test Harness add-on can load and time the tests just like the Talos system can, so I didn’t need to change a thing about the tests. Yes, that means I can add other Talos based page tests too, such as the DHTML and SVG tests.

I addition to some new Talos tests, I was thinking of adding some monitoring to Test Harness. Dietrich has an add-on to collect some UI responsiveness measures. I think we could add something like that to Zippity. Taras Glek has ideas for monitoring memory usage and posting the results once a day. That also sounds like a good use of Zippity.

If you use Zippity / Test Harness and have ideas, comments or found bugs – let me know. Comment here or join Mozilla IRC and look for “mfinkle” in #mobile (or several other channels).

Updated: I fixed a problem with the Pageload test manifest preference. It was pointing a 404 so the pageload tests wouldn’t work. The add-on is fixed now. Thanks AaronMT.

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