Run Multiple Versions of Firefox at the Same Time
[ 13 May 2011 ]
Marked under mozilla, time savers.

Have you ever had the need to run more than one version of Firefox at the same time? Say you’re a web developer and you want to see a site in Firefox 2, 3, 3.5 all at the same time. Don’t worry, you don’t need another computer or any fancy screenshot website to show you the goods. The key is in easily customized portable apps.

Download Portable Firefox

The key to this trick is to download as many portable versions of Firefox as you need. Download the specific versions of portable Firefox that suit your needs:

• Firefox Portable 3.6.17
• Firefox Portable 3.5.19
• Firefox Portable 3.0.19
• Firefox Portable 2.0.0.20

Next, install them to a good common spot. I personally install to a Portable Apps folder with the version number in the name, e.g. C:\Portable Apps\Firefox 3.5\

Customize Portable Firefox for simultaneous instances

You should have all of your different versions in a single folder:

Go into a version and open the Other folder:

Open the Source folder:

Copy the FirefoxPortable.ini file:

Paste the file back in the main version folder:

Right-click and edit FirefoxPortable.ini:

By default, AllowMultipleInstances is set to false:

Set it to True and save the file:

You can now run FirefoxPortable.exe while another Firefox is running. If you follow these steps for every portable version you can run any at the same time.

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