Note: Turning off the automatic update of Firefox is not recommended. Only the latest version of Firefox gets regular security updates and will keep you safe and sound on the internet.

However, if you really need to turn off the automatic update of Firefox, please follow these steps: In the Firefox window, click the Firefox button at the top, then select the Options menu item.

1. If no Firefox button is shown, click the Tools menu at the top of the menu bar, then select Options.
2. From the Options window, click the Advanced panel.
3. In the Advanced panel, click the Update tab.
4. Under Firefox updates, select Never check for updates.
5. Now click the OK button to apply the changes.

That's the problem - I've already done that and Firefox is still trying to automatically update!

Application Basics

       Name
       Firefox

       Version
       12.0

       User Agent
       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20100101 Firefox/12.0

       Profile Directory

         Show Folder

       Enabled Plugins

         about:plugins

       Build Configuration

         about:buildconfig

       Crash Reports

         about:crashes

       Memory Use

         about:memory

 Extensions

       Name

       Version

       Enabled

       ID

       McAfee ScriptScan for Firefox
       14.4.1
       false
       {D19CA586-DD6C-4a0a-96F8-14644F340D60}

       McAfee SiteAdvisor
       3.4.1.195
       false
       {4ED1F68A-5463-4931-9384-8FFF5ED91D92}

 Important Modified Preferences

     Name

     Value

       accessibility.typeaheadfind.flashBar
       0

       browser.cache.disk.capacity
       1048576

       browser.cache.disk.smart_size.first_run
       false

       browser.cache.disk.smart_size_cached_value
       1048576

       browser.places.smartBookmarksVersion
       2

       browser.startup.homepage
       http://www.google.com/

       browser.startup.homepage_override.buildID
       20120420145725

       browser.startup.homepage_override.mstone
       rv:12.0

       browser.zoom.full
       false

       extensions.lastAppVersion
       12.0

       network.cookie.prefsMigrated
       true

       places.database.lastMaintenance
       1339396488

       places.history.expiration.transient_current_max_pages
       104858

       privacy.sanitize.migrateFx3Prefs
       true

       security.warn_viewing_mixed
       false

 Graphics

       Adapter Description
       NVIDIA GeForce GTX 560 Ti

       Vendor ID
       0x10de

       Device ID
       0x1082

       Adapter RAM
       1280

       Adapter Drivers
       nvd3dumx,nvwgf2umx,nvwgf2umx nvd3dum,nvwgf2um,nvwgf2um

       Driver Version
       8.17.12.9573

       Driver Date
       2-9-2012

       Direct2D Enabled
       true

       DirectWrite Enabled
       true (6.1.7601.17789)

       ClearType Parameters
       ClearType parameters not found

       WebGL Renderer
       Google Inc. -- ANGLE (NVIDIA GeForce GTX 560 Ti) -- OpenGL ES 2.0 (ANGLE 1.0.0.963)

       GPU Accelerated Windows
       3/3 Direct3D 10

       AzureBackend
       direct2d

I cannot find anything in your system information that would indicate that the value for updating was ever changed.

Please do the following:

1. Enter about:config in Firefox and press Enter.
2. Dismiss the warning that appears.
3. Set app.update.auto and app.update.enabled to false.

See if that helps!