Running Firefox and Firefox Portable at the same time

This is one of these throw away posts that I place here more for myself than for you guys. This way I know how to do this next time around. I wanted to talk about running two instances of Firefox at the same time. More accurately, an installed Firefox instance and Firefox Portable instance side by side. Why would you ever want to do that?

There are many reasons. For example, you might want to use the Tor Browser Bundle to do some anonymous browsing without actually needing to close your main browser window. Or you may want to use your portable browser to sign into the same website using different credentials. I’m sure you have been in this situation before – you are working on a website and you are signed in as administrator. The feature you are coding will only be visible to no-admin users. Wouldn’t it be nice to simply be able to open a new instance of Firefox and sign in as a non-admin without having to log out?

A lot of people think that Firefox Portable would solve this issue – it is a specialized build after all and it uses it’s own profile and cache and extensions which are stored in a completely different place from the other Firefox. There is no possible overlap between the two. But the Portable version will still refuse to run if it detects that another copy of Firefox is already running.

There is a way around this though. Your copy of Firefox Portable should have a file named FirefoxPortable.ini in it’s directory.

Firefox Portable .ini File

Firefox Portable .ini File

If you don’t see that file, it may be located in the Other/Source folder. If it is, you will simply need to copy it back to the root directory where the Firefox Portable executable is located. Once it is there, you will need to open it with a text editor and change a single value inside:

Modify the .ini file

Modify the .ini file

Locate the following line:


And change it to:


That’s it! Next time you try to open Portable Firefox it won’t be checking for a running instance and will happily coexist with an installed copy.

Running two instances of Firefox at the same time

The solution I posted above only works with the portable version of Firefox. What if you want to run two instances of your installed Firefox? Well, then you need to use profiles.

As you may or may not know, Firefox allows you to define distinct profiles. Each one gets it’s own configuration folder for extensions, bookmarks and settings. You can open the profile creation dialog by running your Firefox with the --profilemanager attribute:

"C:Program FilesMozilla Firefoxfirefox.exe" --profilemanager

On most unix based systems (linux, unix, bsd, osx – ie. everything that is not windows) you can usually get away with:

firefox --profilemanager

This is because the firefox binary will usually be in your path. This will open the profile manager dialog and it will let you create a new profile. Make one with all the default settings then close firefox. Next you need to open with some more attributes:

firefox -P profilename --no-remote

The -P tag specifies the profile name which goes right after it. The --no-remote attribute prevents Firefox from checking whether or not another copy is already loaded into memory. This way you will be able to run two separate instances of the browser – each with it’s own cache, extensions, bookmarks, config and it’s own sessions.

You probably might want to create shell script or a shortcut which will run the second instance this way for you. This trick does not require a portable firefox version. It will work with a single installed copy.

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9 Responses to Running Firefox and Firefox Portable at the same time

  1. Matthew UNITED STATES Mozilla Firefox Windows says:

    I believe there are several Firefox extensions that will allow you to do this in different tabs. For example, CookieSwap lets you switch to a different set of cookies – useful if you want to be logged in to two email accounts at once.

    I’ve never needed this capability, so I can’t recommend from personal experience – maybe someone else has a better extension to recommend?

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  2. Hector SPAIN Mozilla Firefox Ubuntu Linux says:

    I do use the -P –no-remote trick to be able to test a webpage with FF2 and FF3 at the same time, and also with different profiles (dev profile full of extensions, test profile as clean as possible). Really usefull, but I tend to get lost when having more than two different instances open. :-)

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  3. Ray AUSTRALIA Mozilla Firefox Windows says:

    ace tip… it!!!

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  4. Dan UNITED KINGDOM Mozilla Firefox Windows says:

    Thanks, just what I was looking for.

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  5. ez UNITED STATES Google Chrome Windows says:

    Man! I was wondering about this for a while, thank you so much for saving me soooo much time. Really appreciate it!

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  6. dumb Mozilla Firefox Windows says:

    Thanks for sharing…

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  7. someuser SLOVENIA Mozilla Firefox Windows says:

    Thank you.

    This is exactly I was looking for.

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  8. Sukhoi BRAZIL Mozilla Firefox Windows says:

    Thanks for the tip.
    I was trying many ways to do this without any success.
    The trick is to copy Firefox Portable.ini for its subfolder to the root folder, and then set ‘true’ for multiple instance

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  9. Emilio ARGENTINA Mozilla Firefox Windows says:

    Thanks! just what i was looking for!

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