Help wanted: Firefox OS UA detection

Firefox for Android and Firefox OS, while based on the same Gecko platform, have one key difference with respect to compatibility: their user agent (UA) string. The difference between the UA strings for these two products is the inclusion of the “Android” token in the Firefox for Android UA. The lack of an “Android” identifier for Firefox OS is a good thing, in that it provides sites that employ UA detection to detect Firefox OS as a non Android device and subsequently suppress their Android specific endorsements. However, our research has shown that a large number of sites detect the presence of the “Android” token rather than the “Mobile” token to indicate that a client is a mobile device. Firefox OS, therefore, is frequently misidentified as a non mobile device and served desktop content.

For the initial launch of Firefox OS, we created an UA override mechanism the allows Firefox OS to identify itself as Firefox for Android. This mechanism ensures that Firefox OS receives mobile content for top sites. However, this mechanism is a short term solution and does not scale to the scope of the Web. What we want is to clear out this list by having sites recognize Firefox OS as mobile.

The UA override list currently contains 132 entries. All of these sites have undergone some measure of quality assurance from Mozilla or one of our partners and each has been demonstrated to be functional on Firefox OS.

Here’s where we need your help.

Do you, your friend, your relative, or other acquaintance work for one of the sites on this list? If so, please speak with them about changing the site’s UA detection to recognize Firefox OS. If UA detection is to be used, Mozilla’s recommendation is to detect the “Mobi” token, which will allow for the identification of the greatest number of mobile clients.

For your reference, the Firefox OS UA is:

Mozilla/5.0 (Mobile; rv:18.0) Gecko/18.0 Firefox/18.0

Don’t know anyone at any of these sites but would still like to help? Look for other ways to contact the sites. Other ways that we have found to be effective are to ping the site on Twitter, submit a trouble ticket via the site support or feedback forms on their website, or try e-mailing catchall addresses like

The open list of sites with UA overrides can be found in Bugzilla. For your reference, I have also listed the sites that currently have an UA override below.

2013-09-03 Update: Further overrides removed.

2013-03-06 Update: Great support and progress thus far! I will cross off the sites on the list as they are fixed.


About Lawrence Mandel

Firefox program manager
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22 Responses to Help wanted: Firefox OS UA detection

  1. Leonard says: is in reality Telefonica in Venezuela you should probably tell them

  2. Leonard says:

    I will try to help with the others .ve domains, the web is the platform

  3. Henry Avetisyan says:

    Is the reference UA correct? I thought the last 18 should be 18.0

  4. Why not make the UA string contain ‘FirefoxOS like Android’, mirroring WebKit’s ‘AppleWebKit like Gecko’? That would save evangelists’ time for dealing with more serious issues.

  5. Pingback: Web Standards Project Shuts; Not Paying Attention? | Hacking for Christ

  6. Kate Kirby says:

    A very helpful article from the other side of things! I’ve forwarded it on to the maintainer of HTTP::BrowserDetect, the perl module we use at (and a lot of other people use too) to do this kind of thing.

  7. I’ve contacted and will contact the sites too.

      • said that they’d have to test it on a device before making the change :(.

        I’ve contacted most of the sites but not much progress, this is the tally:
        Acknowledged receipt and are considering the change:

        No reply yet:

        Sites I couldn’t contact:

      • Rodrigo – Thank you for the great work contacting all of these sites. For Bing, did you suggest testing in the simulator?

  8. I tried out using the simulator and forcing firefox OS UA and it’s already working. shows desktop if you’re not logged in and mobile when you are. and (google owned) show mobile sign-in but desktop sign-up. I’ve contacted a friend in google about those.

  9. Leonard says:

    Lawrence, if you can confirm these two and are fixed, I’m going to do the patch for gaia.

    Also I’ve been in contact with la and maybe next week, and mercadoli(b|v)* they take this bug by twitter.

    Last there’s a new site with problems but I made a first contact but because they use a plataform provided by another party I’m waiting to contact them

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