By Craig Buckler

What’s New in Firefox 15

By Craig Buckler

It’s that time again. Firefox 14 is officially an ‘old’ browser; it’s time to welcome Firefox 15 to your PC.

I liked version 14. Improvements had been coming steadily, but this release felt more stable and slicker than before. Bar a few minor Flash quirks, everything worked well. Can Mozilla build on that success? I think they have — especially if you’re a web developer…

Responsive Design View

Ooo — a cool new feature! While there are several online and bookmarklet Responsive Web Design tools, Mozilla is the first vendor to build a viewer directly into the browser (menu > Web Developer > Responsive Design View):

Responsive Design View

A range of typical resolutions can be selected or you can drag the (hard to see) resize control at the bottom-right of the box. It’s simple, yet effective. You’ll never need to resize the whole browser window again.

Inspector Layout View

A box layout view has been added to the page Inspector (menu > Web Developer > Inspect, then click the blue bar in the bottom right):

Inspector layout view

The graphic indicates the widths and heights of the box, padding, borders and margins. It’s a feature available in Firebug and several other add-ons, but it’s useful to have it in naked Firefox installations.

JavaScript Debugger

Firefox finally has its own JavaScript Debugger! (Menu > Web Developer > Debugger):

JavaScript Debugger

To be fair to Mozilla, their Venkman debugger has been available for over a decade but development halted several years ago. Again, JavaScript debugging is available in Firebug but the native alternative is likely to be faster — especially if you’re only concerned with scripting issues.

Unfortunately, the debugger does not work correctly yet. It’s fine if you apply breakpoints to timer functions and event handlers, but it disappears and wipes your settings as soon as you refresh the page.

I’ll revisit the feature in v16 — especially since remote mobile debugging will be implemented.

Silent Updates

Firefox 15 may be the last update you ever know about. From this point forward, all updates will occur in the background à la Chrome.

This is good news for developers: most Firefox users will migrate to the latest version quickly and painlessly. Systems administrators may be less pleased; a new version could break a mission-critical application — although automatic updates can be disabled.

I just hope it’s a little more efficient than Google’s updater which can hog slower machines for 10 minutes or more.

Miscellaneous Improvements

Still feeling underwhelmed? Perhaps one of these improvements will put a smile on your face:

  • the word-break CSS property: normal (default word breaks), break-all (breaks between any character) and keep-all (no word breaks)
  • optimized memory usage for add-ons
  • a new JavaScript-powered PDF viewer (you need to set pdfjs.disabled to false in about:config)
  • the web console has received a performance boost
  • support for SPDY networking protocol v3
  • a new high-precision event timer
  • WebGL enhancements with compressed textures for improved performance
  • native support for the Opus audio codec
  • played attribute support in audio and video which indicates the range that has been played
  • the source element supports the media attribute
  • localization for Maithili.

Firefox 15 is a great update. Mozilla may have lost ground to Chrome, but Firefox remains a capable browser which improves with every release. I wouldn’t want to develop web code without it.

Firefox 15 is available for Windows, Mac and Linux PCs. You possibly have it already but, if not, head over to

  • viktor

    sorry.. on AMD PHENOM II X4 960T 3GHZ, 4GB RAM slowest program on my pc.. sometimes opening a new tab take 30 seconds.. = MEGA ROFL LOL..
    new, original, clean install windows 7 ;)

    • That’s definitely not normal. I have 6 computers with FF at home, and 4 at work. Windows, Mac, and Linux. None have slowness issues with FF.

    • Rune Jensen

      On Linux, no problems what so ever, very fast program.

      I just whish they made the viewing area larger as in chrome. And they should built-in NoScript instead of making it an extension.

    • Dan

      Try creating a new Firefox profile. I had this problem for a while on my mac and it was caused by something wrong in the profile files. FF flies now!

  • Slowly, but surely Firefox is catching up

  • Not hating on Mozilla, more of a fan, though Chrome has had a response design view feature for a release or two.

    Developer Tools > Click the Cog in the bottom right > User agent > Override device metrics

    • Mmm. While that’s handy now and again, I wouldn’t say it’s a particularly usable tool aimed at RWD testing. Thanks for the reminder, though.

  • Thanks Craig,
    you just helped us to spare some valuable time. I’d just spread the word…

  • System administrators can also use the esr (extended support release) update channel for Firefox –


    I followed your instructions on opening the New Inspector Layout View and it loaded fine.

    As soon as I hit the “Style” button in the bottom bar the Inspector Layout stretched so far to the right I can’t even see the “Style” panel and I can’t even get the Inspector Layout View to go back to normal.

    Ugg is there any way to reset the Inspector Layout View???

    I can screenshot my problem if that would help?

  • i feel it ‘s best and nice. and very fast. :)

  • Rodrigo M

    I do not have a Layout Inspector option on my mac. Running Lion. Anyone else having this problem?

  • Jan

    Really fine to get media attribute on the source element.

  • Wonderful Article! Yeah Its fine Mozilla Firefox 15 but its catching very slowly as compared to i always prefer to Google chrome.Well Thanks for sharing this post.

  • I still can’t use firefox to watch videos or youtube. Not really all that impress with what they did.

    • Tom Miller

      Jim you have to have something else wrong. I have never had any trouble watching videos or youtube on firefox. I belong to netflix and stream video from that site all the time and they use silverlight to display the vids. No problems.

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