Firefox 9 Features, Changes

Martin Brinkmann
Oct 1, 2011
Updated • Dec 2, 2012

With the release of the stable version of Firefox 7, or more precisely Firefox 7.0.1, came also updates to the beta, aurora and nightly channels of the browser. Each channel has been bumped up a version. Firefox Beta to 8, Firefox Aurora to 9 and Firefox Nightly to 10.

Whenever Firefox Aurora gets a bump, I write about the new features and changes of the release to give beta and stable users a heads up what they can expect when their channel moves to that version.

Firefox 9 introduces type inference in the browser which improves the browser's JavaScript performance in the two digit range. The Mozilla developer who worked on introducing type inference noticed performance increases of up to 44%, independent testers results between 20% and 30%.

The few remaining features and changes are not that spectacular. Mozilla notes that the browser is now supporting the new application toolbar and icon styles of Mac OS X 10.7 Lion as well as multi-monitor support and two-finger swipe navigation gestures on the operating system.

firefox 9 features

Web developers can make use of JavaScript DNT Detection which detects if a user has opted out of behavioral tracking. The only other feature is supported for chunked XHR requests which can be utilized to display "data as it arrives instead of waiting for an entire download to complete".

Firefox for Android users who can download a version of Firefox 9 for their system as well will notice a lot of changes. The browser now has a new look and feel to it. This includes a new awesome bar design with quicker access both to bookmarks and history items but also to preferences, add-ons and downloads. Back and forward buttons have been added to the awesome bar for easier navigation.

Firefox for Android users will benefit from faster start-up times, especially on devices with slow file systems.

Type inference is without doubt the biggest new feature of Firefox 9. One could say that it is the only end user feature of the desktop version. Only Mac users benefit from additional support for the new Lion operating system.

If you are interested in Firefox 9 you can download it from the Future of Firefox website for desktop and mobile devices.


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  1. Genious said on October 3, 2011 at 4:39 pm

    I see where they are going, but they are headed there too fast. They are not focusing on the problems their updates cause with add-ons, the reason I use firefox.

    I don’t want to add a theme, kill the new browser only to reopen it just to have a theme be there until the next time it restarts. I did not like the fact that i had to download an add-on just so i could see my add-ons.

    Slow down, do it right the first time mozilla.

  2. AC said on October 3, 2011 at 9:42 am

    I really do feel that add-ons are one of the biggest positives when using Firefox but they’re also the biggest negative because of incompatibility and memory leaks.

    As soon as Mozilla can make them compatible by default and highlight when add-ons are responsible for loss of browser performance, then things will get much better for them, very, very quickly.

  3. Rahul said on October 2, 2011 at 4:44 am

    In response to this link,

    what far i have understood is that they will probably initiate a dialog that add on may slow your firefox with some link to understand more about the add on information, why they slow your firefox and possibly a solution.

    I also feel many users aren’t aware about the memory leaks caused by specific addons, they just install blindly and blame firefox for high memory usage.

    Even me too i run CCleaner before shutdown, this helps a lot and firefox never crashed except for some unresponsive scripts.

    Martin you have taken a very good initiative to educate about the features in firefox but i also think you should include some advice on TO DO or TO NOT ADVICE for firefox.
    I really feel sad when they start blaming this amazing open source browser for no good reason.

  4. James Kelly said on October 1, 2011 at 10:02 pm

    Hi AC,
    I know what you mean, I’ve also been looking at the memory creep as well and subsequent builds do seem to be less and not just because there are less extensions loading. I’m also looking at the version on Ubuntu (11.10) and FF 7.0.1 with the same config and FF8 on Win7 is using at least 100kb less.

    Chrome might be getting more popular but its resource usage is hellish at times and it’s claimed to be almost crash proof but I haven’t had a FF crash since 5 beta, except for yesterdays kerfuffle and I think I realise why that was.

    Every night before I shutdown I run CCleaner to get rid of the junk, I think there were old files lying around that needed to be cleared out after the upgrade and they weren’t at the time. So today when I started up I had a clean machine but used the other browser before trying out FF (which I was going to run without add-ons to look for a cause). FF worked no problem and it’s been running since before my second post.

    Hence after the upgrade I should have cleared the old cache and history I think or at least done a reset. Mystery solved I believe.

    Oh the joys (and frustrations) of IT!!!

  5. AC said on October 1, 2011 at 9:08 pm

    Hi James,

    I have been on the beat release channel since late August and I am definitely staying on it. It’s not quite as raw as Nightly or Aurora but it does put you 6 weeks ahead of the final stable release and with no noticeable loss of stability or performance.

    I know FF8 doesn’t seem to have brought in many changes when you read the release notes and various details on Mozilla sites but it does seem that little bit snappier and more responsive than FF7, especially when starting up for the first time, even with 5 tabs. The memory usage seems to have improved a little bit more as well which is excellent.

    1. AC said on October 1, 2011 at 9:09 pm

      *beta not beat!

  6. James Kelly said on October 1, 2011 at 3:31 pm

    Just tried FF8 and all now works perfectly and faster as well. I don’t know what happened so I take back all my earlier comments. Sorry for all the fuss.

    FF8 is back to being my default browser.

  7. AC said on October 1, 2011 at 2:50 pm

    From what I understand, reading the page that I linked to above, FF9 will also show users how well or how badly some of their add-ons are performing. I don’t know how much this will help but I believe it will make it easier for users to see which of their add-ons are slowing down Firefox.

    Potentially it’s awesome as then people can blame the add-ons for the slow downs, not Firefox itself, but we will have to wait and see.

    Martin – If you can tell us any more about this particular feature I would be very grateful – Direct link is here –



    1. Martin Brinkmann said on October 1, 2011 at 3:13 pm

      The feature is not yet implemented in the Aurora builds. I briefly covered the feature here:

  8. James Kelly said on October 1, 2011 at 2:42 pm

    I don’t know what Mozilla have done, I was using nice versions of FF7, 8 and 9 until yesterday when the browser recommended an upgrade on FF7. Which it did cleanly, now my home page (which was set as my Hotmail in-box, isn’t being recognised and MS are telling me to find a new browser (it recommends, IE, Chrome, Safari and believe it or not Firefox!). Also my GMail is only showing up as basic HTML!!!! This is happening on the beta and Nightly channels as well.

    I’ve changed nothing so what’s going on?

    I’m still using the same profile, I haven’t fiddled in “about:config”. What it means to me is I’ve reverted to another browser altogether just to access my mail.

    Contacted on=line support and they didn’t know either.

    Come on Mozilla have you secretly changed some Java settings and not told us? Am I the only one with this problem? Can anyone help because I’m lost on this one.

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