Mozilla: Firefox 5 Release Means EOL For Firefox 4

Martin Brinkmann
Jun 22, 2011
Updated • Mar 15, 2012

The Firefox rapid release process that Mozilla switched to has caused some confusion about continuing support for older versions of the browser. While there was never an official support timeline before and after the process change, it was assumed by many that major versions of Firefox were supported for at least six months after release. Mozilla recently dropped support for Firefox 3.5, and in a somewhat surprising move support for Firefox 4.

Firefox 4, or more precisely its only update Firefox 4.0.1 was released April 28, less than two months ago.

Firefox 5, which has been released yesterday is seen by Mozilla as a security update for Firefox 4. It in turn means three things:

  • Mozilla Firefox 4 users will not get any more updates
  • Firefox 4 users who have not updated yet are running a browser with security vulnerabilities
  • Support for older versions of the browser has been reduced significantly

Some users might say that it is not all that bad. Just update from Firefox 4.0.1 to Firefox 5 and you are protected again, and update again from 5 to 6 and so on. Some arguments speak against this practice. Enterprise users need to do a lot more testing because of the new release process, and users who came to rely on specific add-ons, might have to disable them or force compatibility on them to get them to work in the next major version of the browser.

Mozilla notes that the major version updates are typically less likely to cause incompatibilities and other problems, due to the rapid release process which pushes out smaller releases regularly instead of big releases occasionally.

One thing that I'm personally a bit confused about is whether automatic updates are applied to Firefox 4, or not. I installed a test version, and while it shows a new update for the browser under Help > About Firefox, it does not seem to apply that update automatically when I close the browser and open it again. The Aurora release on the other hand applies updates automatically on every start.

Does that mean that Firefox 4.0.1 or 4.0 users are not getting Firefox 5 delivered as an automatic update? If that is the case, does it mean that Firefox 4 users are running a browser with known security vulnerabilities?

If you are running Firefox 4, I recommend to update to the latest version of the browser immediately.

What's your take on all of this? Let me know in the comments. You can read the lifecycle policy discussion here at


Tutorials & Tips

Previous Post: «
Next Post: «


  1. Dave said on June 26, 2011 at 12:19 am

    What about WebGL flaw that allows hackers?

    See the Register -:
    This applies to FF4, FF5 and the latest versions of Chrome, Safari and Opera that uses WebGL, the advice being given is to disable it in ‘ about:config’.

    If you read the article WebGL don’t give two hoots it seems and Microsoft are avoiding using WebGL , they say for security reasons…. like hell, more like they want to keep their hands ‘on the pot’ so to speak.

    Browsers really aren’t about speed but their ‘usability’ , I guess folks don’t want to be waiting, waiting and waiting… heck the fastest browser may not necessarily be the most ‘secure’ or the most ‘usable’ or adaptable for that matter.

    FF5 just like FF4 requires 512mB of RAM to get going…. Mozilla don’t say if that i with tabs open or not, now that is a big chunk of resources for a browser, thats going to be even more with updates and fixes.

  2. Cattleya said on June 23, 2011 at 2:40 pm

    Hi guys, Firefox 5.0 Final’s Javascript performance seems slower than Firefox 5.0 Beta, it even slower than Firefox 4.0.1.

    Maybe Firefox 5.0 Final remove Ionmonkey JavaScript engine which faster than Google Chrome and Opera ?

    Anyone please let me know ? thank!

    More information:
    Old test: Firefox 5.0 Beta vs Chrome 12, 13:

    Chrome 12 and 13:

    And Firefox 5.0 Final vs Firefox 4.0.1:
    Firefox 5.0 Final:
    Firefox 4.0.1:

    Firefox 5.0 Beta seems much faster, even faster than Chrome and Opera.

    I used Sunspider:

  3. Ryan D. Lang said on June 23, 2011 at 8:20 am

    I recommend Ubuntu users switch to Chromium. As far as I know, Firefox 4 is not officially supported, let alone 5. I had to manually install it from the command line. I switched to Chromium from day one. Updates are automatic. I just checked my version and it matches the most recent stable release.

  4. Rick said on June 23, 2011 at 12:30 am

    The only real issue with the numbering…is with the plugins. Most are set to a max version of 4.x so updates didn’t cause issues; however this moving main version up causes less used addons to become uninstallable without having to edit the xpi file.

    Easy enough to do but a pain that need not be.

    1. Leanne said on June 24, 2011 at 4:28 pm

      True, and to be fair, the common user doesn’t know how to change the xpi file. It’s alright all of us complaining about this as if it is in beta and there all little things that we at least know enough about to sort, but this is a “major release” as far as the public are concerned and they wont be impressed to know that some things wont work. Such as DIVX plus player, I paid for that, and if I didn’t know I cold change the file so it would work, I would probably just switch to chrome.

  5. dwarf_t0ssn said on June 23, 2011 at 12:06 am

    Gonna CCleaner, mozbackup, then try this Firefox “5”.

    This new version numbering gimmick is pretty lame, and only makes me think that there will be more of those horrible changes that always require an extension to get rid of (read: to get your browser back).

  6. Gary M. Mugford said on June 22, 2011 at 11:34 pm

    I upgraded to v5 and it’s got me thinking maybe Chrome needs a look. My main gripe is extensions. As usual, more than a handful are left behind. Evernote, FEBE, ffChrome, Save Image in Folder, Show Go!, Stop AutoPlay and Wired-Marker. I can live without any of them for a period, so It’s not like I declare armageddon. But this ‘transitional’ period gets wearisome. And now that it will occur every six weeks?!? Plus, I actually fear some of them won’t be updated. I’m not optimistic about ffChrome for example.

    That said, if, in fact, the releases are merely updates rather than major releases, then saying v4 is end of life is merely semantics. v5 is really v4.02. If, in trying to ‘fool’ users into thinking they are getting something new and major. And the worst part, because of the version-checking system used in add-ins, it’s just a setting that has cost me temporary use of my preferred add-ins, then I’m ticked off with Mozilla.

    Can’t I have my extensions, the security updates and a v4.02 version?

    1. Jimmy said on June 23, 2011 at 8:27 am

      It likely all your add-ons will work if you disable compatibility checking since there weren’t big changes. The easiest way is to use Add-on Compatibility Reporter:

      It’s also likely that if you hadn’t manually updated you wouldn’t have had to wait long for your add-ons to be made compatible and for Firefox update automatically.

      1. Gary M. Mugford said on June 26, 2011 at 12:37 am


        Have, indeed, added the compability add-on to skirt the issue. The fact is, five days out, the add-ons in question still aren’t compatible. Also, this is all representative of a desire to issue v4.02 as v5 for very little benefit. It is NOT a major upgrade and it doesn’t break many add-ons, if any. Had Mozilla released it as 4.02, I might not have even noticed it had happened. I would have gotten the security updates and been happy with this latest version of the best browser for my needs. Instead, the simple act of re-setting the version number for PR reasons, cost me time, effort and a lot of goodwill. I’m sticking with it, because of the reporter. But, I now have Chrome running full time on the right-hand monitor and I’m using it for more than just the Google sites now.

        You reap what you sow.

        Thanks for taking the time to point out the availability of the Reporter to me and to others, GM

  7. Roman ShaRP said on June 22, 2011 at 8:19 pm

    I switched to Palemoon custom build last year, developer still maintains 3.5 branch, 5.0 still in progress.

    I don’t think that copying Chrome style is good idea, but for now I have no reasons to protest.

  8. bastik said on June 22, 2011 at 7:40 pm

    I read that Firefox 4 users will get Firefox 5 with the regular updates.

    I installed FF5 yesterday, because all my extensions were working. To be honest there’s no real change. That’s not bad, but FF 4.0.2 or 4.1 would be closer to what it looks like and what it feels like. Whiles previous major releases, were different each time, this is no longer the case.

    Memory usage dropped from 4 to 5, but it increased from 3.6 to 4. I guess I’m slightly above 3.6.

  9. vasa1 said on June 22, 2011 at 7:23 pm

    This article (of a few days ago) talks about throttling automatic updates:
    h t t p s :/ / wiki.mozilla. org/Releases/Firefox_5/Risk_mitigation_strategies

    Could that be a reason why not everyone sees that an update is available?

    1. AC said on June 23, 2011 at 1:13 pm

      I just a looked at the link that was posted in the first comment and it does seem that for the first 51 hours following the release of Firefox 5, updates have been throttled or restricted so that not everybody gets them. It seems that Mozilla are concerned about the security, stability and compatibility of Firefox 5.0 and want to see what happens to the first 6 million users that get the update before they release it to everybody.

      From what I can remember I was trying to manually update Firefox all day on Tuesday 21st June and the update finally happened when I got home after work at about 18:00 here in the UK. That would mean that the 51 hour period ends tonight at some point so within the next day or 2 we should see a massive spike in the adoption of Firefox 5.0 depending on what Mozilla decided to do.

      In my opinion they should get it out there as it’s a major security update and it really solidifies the work that was put in to Firefox 4.0. Plus if they want to keep pace with Chrome then they need to update Firefox in the same way that Chrome is updated. Otherwise they have a user base that is fragmented across numerous different unsupported versions of Firefox and that’s a lot harder to manage. It also means that people may move to Chrome, where as if you keep them up to date with the latest version of Firefox then they may stay as a happy and regular user.

      However if they are still on Firefox 4.0 by the time Firefox 10 is released by try Chrome and decide it’s better, then it may be tough to convert them back into a Firefox user once they have gone.

Leave a Reply

Check the box to consent to your data being stored in line with the guidelines set out in our privacy policy

We love comments and welcome thoughtful and civilized discussion. Rudeness and personal attacks will not be tolerated. Please stay on-topic.
Please note that your comment may not appear immediately after you post it.