Mozilla Firefox for U3 Support

Many of the most common issues that arise when using Mozilla Firefox for U3 are addressed here. Please read through the various topics to see if any of them address your question. If you do not find an answer here, you can ask it in the U3 Apps Support Forum.

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Mozilla Firefox for U3-Specific Issues

General Mozilla Firefox Issues

Installing Mozilla Firefox for U3

To install Mozilla Firefox for U3, just download the application from U3 Software Central. Or, download the U3P file at the top of the Mozilla Firefox for U3 page and install it within the U3 Launchpad. To do this:

  1. Click the Download Now! link at the top of the product page and then the FREE link within Software Central to download the file
  2. Save it to your desktop, so it's easy to find
  3. Once it's done, from your U3 Launchpad, click Add Programs and then Install From My Computer
  4. Browse to your desktop and then double-click on mozilla_firefox_for_u3_1.0.7.u3p
  5. Click Next and wait for the application to be installed
  6. Click Done when finished

Using Mozilla Firefox for U3

To start up Mozilla Firefox for U3, just click Mozilla Firefox for U3 within your U3 Launchpad and then use Firefox as you normally would. There are a couple minor changes from a standard version of Firefox that are important to keep in mind:

  • No Browser/Download History - History is turned off by default to reduce wear on your device. You can enable in within Tools - Options - Privacy if you'd like.

Installing Extensions

Nearly all extensions work well with Mozilla Firefox for U3. You may occasionally encounter issues installing extensions directly from non-official sites (sites other than, etc). If this occurs, do the following:

  1. Save the extension locally by right-clicking on the link to the .xpi file and selecting Save Link As
  2. Open the file you just saved within Firefox by selecting File - Open and browsing to it
  3. Follow along as with a normal extension installation

Some extensions' download links are harder to find and will be provided here (right-click and save):

Upgrading Mozilla Firefox for U3

Upgrading Mozilla Firefox for U3 is a snap. Just download the newer version from within U3 software central or using the directions here under Installing Mozilla Firefox for U3 and install it right over your current version Mozilla Firefox for U3. (Do not remove your existing copy in either case.) All your bookmarks, settings and extensions will be saved. Your installed plugins will be reset to the default, so you will need to reinstall Flash, Shockwave, etc. This will be addressed in an upcoming release.

Copying Your Local Firefox Settings

If you're using a local copy of Firefox, you may wish to just copy your local Firefox settings right into Mozilla Firefox for U3. Your local Firefox profile is usually installed in a directory like C:\Documents and Settings\[user]\Application Data\Mozilla\Firefox\Profiles\default.???\ Just the contents of that directory (except the cache directories) to the profile directory within Mozilla Firefox for U3. This directory is located on your U3 device within ?:\System\Apps\3C9F7B3F-D55C-42cd-8537-B878518B73AF\Data\profile. When you start Mozilla Firefox for U3 for the first time, be sure NOT to set Mozilla Firefox for U3 as your default browser. Also, be sure to turn off disk cache, password saving and history if you're using a non-hard drive portable device. You can set all of these within the Privacy tab of the Firefox Options window.

Installing Plugins (Flash, Shockwave, etc.)

With Mozilla Firefox for U3, plugins work a bit differently than they do in regular Firefox. You'll need to manually install them into Mozilla Firefox for U3. Here's how to do some of the most common plugins:

  • Flash Plugin - To install Flash, follow these steps:
    1. Flash is available as an extension. Just click the link.
    2. You'll probably see a yellow bar across the top of the browser (if not, skip to Step 5), on that bar, click Edit Options
    3. In the popup window, click Allow to add to your whitelist and then click close
    4. Now try the link again
    5. You'll see a popup asking if you would like to install, click OK after the countdown and follow along the prompts
  • Shockwave Plugin - To install Shockwave, follow these steps:
    1. Download the free Shockwave Player from the Macromedia website
    2. Run the installation routine and, instead of letting it install to a local browser, select to choose your browser
    3. Browse to X:\System\Apps\3C9F7B3F-D55C-42cd-8537-B878518B73AF\Exec\firefox (where X is your U3 device's driver letter) and continue with the installation
    4. You may need to restart Mozilla Firefox for U3 for the changes to take effect
  • Other Plugins - Other plugin directions are coming soon...

Configuring Proxies

As you move between different computers, you may encounter systems on networks that use proxies and don't allow direct access to the internet. You'll need to update Mozilla Firefox for U3's connection settings to use in the new environment. You can find these settings within Tools - Options - General - Connection Settings. If you routinely use PCs with different proxy settings (for example, work and home or work and school), you can set up the options for both and easily switch between them with the SwitchProxy extension. If you need to determine the connection settings of the PC you are on to add to Firefox, just run our Proxy Get Utility and it will let you know what they are.

Known Issues

The following are known issues with this package:

  • Trojan/Virus detected - AntiVir and Avast sometimes find a trojan or virus in the launcher or within the application itself. This is due to an error within the product and should be addressed by your antivirus software provider.
  • No Portable Java - Sun's Java VM needs to be installed locally. There is currently no way to make it portable at present, so you will only be able to use Java-enabled sites on machines that have the Sun Java VM installed locally.

Modifications (Mostly of Interest to Programmers)

I made some modifications to the default ZIPped version of Firefox to make it more USB key friendly (decreasing total install size and the number of writes to the drive, which will increase drive life). These changes are listed here so you'll know what they are, and so you can recreate the process, if so desired. Obviously, you can change many of these settings (ex cache, form saving ) by changing the options in Firefox, but you will increase the number of writes to your flash drive, thus decreasing its life.

  • Extension-Friendly Launcher - A specialized launcher based on Portable Firefox is included with Mozilla Firefox for U3. It automatically makes your extensions portable.
  • Default Profile - A default profile exists within the firefox directory.
  • No Default Browser Check - Firefox won't check to see if it is the default browser on startup.
  • Download Prompt - Firefox will ask where to save downloads.
  • Download History Cleared - Download history is cleared on exit.
  • Browser History Disabled - The history has been disabled to decrease disk size and the number of writes to the disk, increasing disk life.
  • Form Info Saving Disabled - Information from forms is not saved.
  • No Disk Cache - The browser disk cache has been disabled to decrease disk size and the number of writes to the disk, increasing disk life.

Version History

Mozilla Firefox for U3 is based on Portable Firefox which grew out of a mozillaZine forum topic (now split in two: original, followup) back in June of 2004.

  • - July 21, 2006
    • Updated to Firefox
    • Fixed issue with desktop in File Open/Save appearing on U3 device
    • Added multi-launch ability
    • Improved Safe and Unsafe Eject handling
  • 1.0.7 - November 21, 2005
    • Initial Public Release