Firefox 4.0.1 Has Been Released

Martin Brinkmann
Apr 28, 2011
Updated • Dec 14, 2014

Mozilla is currently distributing an update for the Firefox 4 browser to worldwide mirror servers to be prepared for the update rush once the updating notification appear in the web browser and on the official project homepage.

For now, no sign of the update is visible on the homepage or in form of notifications in the web browser. Only the official ftp server is already carrying versions for all supported languages and operating systems.

The beta release notes classify Firefox 4.0.1 as a security and stability release. Bugzilla lists a total of 53 bugs that have been fixed in the latest Firefox release. Of those, 12 have received a severity rating of critical, another 9 one of major.

The majority of critical issues have been crash and freeze related, only two address other issues. Other notable fixes include a issue where Adobe pdf documents with a size larger than 5 Megabytes could not be loaded in the browser, problems with the address bar and other text edits after loading pdf documents using Adobe Reader X and the inability to refine searches on Yahoo answers.

It can take up to 24 hours before the release is officially announced on the homepage and via the browser's built-in updating functionality. It is likely that download portals such as Softpedia or Major Geeks will be faster and offer the download on their sites before the official announcement.

Since it is a security release it is important to update the web browser as soon as possible. A good starting point is the list of official Mozilla Release Mirrors which often provide access to downloads for all languages and operating systems before the final release announcement on the Mozilla Firefox website. The release notes are accessible here.

All Firefox 4.0 users are asked to update the browser to the new 4.0.1 version as soon as possible to protect it from attacks targeting the vulnerabilities.


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  1. Karen said on May 5, 2011 at 5:22 pm

    I tried to download the yahoo toolbar and was told it is not compatible with firefox 4.0.1. This needs to be fixed as I think that is why I just had to send my new computer to be fixed as the hard drive got fried while trying to send an email to yahoo via yahoo mail. I lost everything. Thank you Yahoo and Firefox.

  2. Kelly said on May 3, 2011 at 11:44 am

    My Yahoo Toolbar no longer works with the new Firefox 4.0.1. Are you going to fix this????

  3. Mitch said on April 30, 2011 at 7:40 pm

    Firefox 4.0.1 is crashing when going to yahoo email. Did the same under 4.0

  4. Daily Software Update said on April 29, 2011 at 10:56 am

    Thanks For Update i love firefox

  5. Ashley Pearson said on April 29, 2011 at 12:10 am

    Nice to see its all being sorted out!

  6. boris said on April 28, 2011 at 11:34 pm

    I am not sure but quality of Firefox 4.0.1 are even worse than ones in 4.0. Or is just my eyes.

    Can anything be done to make Firefox fonts not suck?

    1. Martin Brinkmann said on April 28, 2011 at 11:50 pm

      You can disable hardware acceleration if you have not already. See here

  7. bastik said on April 28, 2011 at 9:31 pm

    Thank you.

    I was looking for “Update Firefox” to, but I looked at “About Firefox” because I expected it there. Well no update available yet.

    What’s an “Adobe pdf document”? Did it only effect Adobe or alternative viewers, too?

    1. Martin Brinkmann said on April 28, 2011 at 9:56 pm

      Bastik if a pdf is opened via Adobe’s plugin in the browser.

      1. bastik said on April 29, 2011 at 7:05 pm

        Thank you for clarifying that.

  8. Qiu said on April 28, 2011 at 9:27 pm

    Just checked my firefox, it is 4.0.1 already. I am sure I updated several days ago.

    1. Rick said on April 28, 2011 at 10:09 pm

      They pulled the original 4.0.1 – no reasons provided – it was released on April 26 for a few hours.

  9. DanTe said on April 28, 2011 at 8:59 pm

    Thanks Martin. That’s one dumb, non-intuitive design on Firefox’s part.

    1. gwt said on April 29, 2011 at 6:18 am

      You’ll get used to it.

  10. DanTe said on April 28, 2011 at 8:16 pm

    I just noticed something. There’s no “Check for update” in the menu items of Firefox 4.

    1. Martin Brinkmann said on April 28, 2011 at 8:19 pm

      You need to click on Help > About Firefox for that now.

      1. Rick said on April 28, 2011 at 8:45 pm

        and the update isn’t available that way yet…

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