Are you posting from the problem machine ? Your system info aside indicates that you are already using Firefox 10.0 have a look using

• Firefox button -> Help -> about Firefox
• or key about:support into the location bar and go to that page to see info including version number.

What version does that show that you are using ?

P.S. note that a new version Firefox 10.0.1 is to be released very soon probably Friday 9th Feb, (to resolve some problems including startup crashes) so do not be surprised when another update is offered.

No, I posted this from a Windows 7 desktop running Firefox 10.0. This is not the machine that was showing the issue.

Check what your other machine shows it is using. Also use about:support to look at the user agent string it says it is using.

I can possibly understand firefox 3.6 or similar trying to upgrade and failing, but do not see any reason why firefox 10 would try to revert to firefox 3.5, other than maybe a system restore to an earlier date when that was the current version.

( I wonder is there any posibility Windows on reboot is resorting to using an ancient last working configuration - are other files and applications still current)

Which security software (firewall, anti-virus) do you have?

Some have virtualization features that may cause files to get reset on a reboot.

I've been using the rolling updates for a long time. I thought I had had a dodgy upgrade which was causing this issue, so last Friday, I uninstalled Firefox and all plugins, and made sure the install directory was deleted. Then I installed Firefox 10.0 again.

Today, I've been downgraded to 3.5 again (this time without a reboot). Can somebody help me in posting some diagnostic info from Firefox 3.5? Using about:support doesn't seem to work, as it doesn't recognize the URL.

Hi Cor-el, Firewall is plain old Windows XP Firewall. Anti-virus is Symantec Anti-virus 10.1.5.5000.

about:support is also accessible from the drop down menus as troubleshooting info

• Help -> Troubleshooting information

P.S. It also occurs to me that you may just be seeing a page about firefox 3.5 rather than using firefox 3.5

• are you able to see the Firefox button (you may need to you turn off the menubar toolbar by using
  • View -> Toolbars []menubar
• please attach a screen shot from the computer that downgrades to firefox 3.5

@John99 Neither about:support nor Help->Troubleshooting information are available on Firefox 3.5

The about box states: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1) Gecko/20090624 Firefox/3.5

I have not got firefox 3.5 available, my earliest version is 3.6. The info you have posted seems to confirm it is 3.5 information.

Or maybe it is still Firefox 10 but with a lot of changes made, try running in the default theme and safemode.

• see safe mode regarding starting in Firefox's safe mode
• whilst in safemode also disable all plugins
• see also troubleshooting extensions and themes

I uninstalled firefox completely, including removing any remaining files in c:\program files\Mozilla Firefox\

I re-installed Firefox 10.0.1, and began slowly re-introducing my plugins. Today I encountered another downgrade to 3.5, with the following plugins enabled: -Adblock Plus 2.0.3 -Flashblock 1.5.15.1

I suspect one or other (or both) of these as part of the problem. This only happens on Windows XP, as I have the same setup on Windows 7 without any issues.

The difficulty in testing this, is that it can take several days to become apparent. I can install firefox and plugins and work happily for a few days before a downgrade occurs. I don't seem to be able to recreate the issue at will yet.

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I see you already tried a clean install (I uninstalled firefox completely, including removing any remaining files in c:\program files\Mozilla Firefox\...) but another possible solution might be another uninstall, then reboot the computer and do a custom install of Firefox 10.0.2 (available from www.mozilla.org/firefox if you need to re-download it) into a different program folder, such as C:\Program Files\Firefox

P.S.

Hi Alice, I'll give that a go, and see what happens.

Another working theory of mine is that when new updates are pushed to the release update channel, some snafu is causing me to downgrade. I don't know how to prove/disprove this though. It could account for why downgrades don't happen immediately when the 'conditions' are right, but seem to wait a while.

Does your Windows XP computer have multiple Windows user accounts? Are both admin accounts? I just came across a related discussion on that as a possible cause of upgrade problems, but in that case, the upgrade failed to complete, with an error message.
Ref: http://forums.mozillazine.org/viewtopic.php?f=38&t=2393159 Difficulty upgrading Firefox due to "other copies"

Yes I have two local, and one domain user in the Administrators group. I usually log in using the domain account, and I'm the only user. The other accounts are used by our IT dept., infrequently for administration. I'm the only user on the laptop who has installed and uses Firefox, or indeed the laptop as a whole with any frequency.

I don't use multiple Windows user accounts so your best bet would be to wait for someone else to help but, you might want to try updating the other user accounts to Firefox 10 or else uninstall Firefox for those users if they have Firefox 3.5 installed, since it's an insecure browser.