I have been using Firefox 3.6.6 ever since my build was updated a few days ago. And now when I heard of Firefox 4.0 Beta 1 being released I thought of giving it a try. What really had me stuck was that whenever I ran firefox.exe from the nightly build (Firefox 4.0 Beta 1), it ran the same Firefox version that I was previously using i.e. 3.6.6. I had no intentions of parting with my add-ons and settings for the current stable build and replace it with nightly, so I started looking for the solution, to run both the builds without either of them interfering with the other.


Firefox uses profiles to manage user settings, bookmarks and extensions. When, for the first time, Firefox is installed a default profile is created along with the install. If more than one build is installed on a system, both by default use the same profile folder thus using the same profile. As the builds are different many a times there is a problem with compatibility of add-ons and general settings.

So, to solve this particular problem this is what is to be done.

  1. Open run (Win+R).
  2. There locate the path of firefox.exe by clicking on the browse
  3. Once located the content of run prompt would change to”C:\\Program Files\\Mozilla Firefox\\firefox.exe
  4. Add the following attributes to already written path“C:\\Program Files\\Mozilla Firefox\\firefox.exe” -p -no-remote
    and press enter.
  5. This will open User Profile Manager.
  6. In User Profile manager a profile could be found named as “default”, unless you chose to change previously.
  7. Now all you need to do is to rename your existing profile to something other than default and then create a new profile of any name that you may like.

As for this post, i have renamed my default profile as ‘old’ and then created a new profile called ‘new’.


The above process replaces the default profile with the profile name that you want to keep, which obviously could be renamed later. Now create a shortcut of both the builds on the desktop and carefully choose the build which u are using and open the shortcut properties, by right clicking on them.

The shortcut of the newly installed build will have a “Target” path somewhat different to that mentioned above.

As for my case the path is “C:\\Program Files\\Mozilla Firefox 4.0 Beta 1\\firefox.exe”

Change the path of the Target field of the shortcut’s property to

…\\firefox.exe” -p new -no-remote”

Similarly for the old build, the Targe path will have the path previously located. Change the Target field of the shortcut’s property to

“…\\firefox.exe” -p old -no-remote”


All right now you are ready to go. Rename the shortcuts so that you are able to differentiate between them and you are done. Clicking on either of them will open the respective builds.

To revert back to previous state all you need to do is to uninstall the new nightly build first from the control panel and then perform the step 1-5. Then rename the profile old to default and Firefox will work as before.

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A full time developer and a part time blogger, but above all a person with extreme passion about anything with a 'Tech'. You can find him at UjjwalKanth.com, and follow him at @ujjwalkanth