Firefox is a great browser, but one thing it doesn’t let you do is open multiple instances of it. This can be useful say, if you have a dual-screen computer or if you’re a beta tester and would like to compare versions of Firefox. For me, Firefox won’t let me open more than one window from the Start bar, so I use this trick to pass that restriction.

To allow the running of multiple instances, follow these steps:

Windows PC

1. Open Notepad or a basic text editor
2. Copy-paste this into the editor:

   @echo off
   set MOZ_NO_REMOTE=1
   start "" "C:Program FilesMozilla Firefoxfirefox.exe" -p
   set MOZ_NO_REMOTE=0

3. Save the file with a .bat extension at the end. Use whatever name pleases you.
4. Click on the .bat file (instead of the Firefox shortcut) to open Firefox. The Profile Manager will appear, allowing you to choose a profile.

Mac OS

1. Open Terminal
2. Enter the following command, which will open up the Profile Manager:

   /path-to/Firefox.app/Contents/MacOS/firefox-bin -Profilemanager

3. For each new instance of Firefox that you want, click the Create Profile… button to create a new profile.

There are additional steps that make profiles auto-launch, which will better simulate running multiple instances:

4. Open up the Finder, and navigate to where the instance of Firefox that you want to set up is located.
5. Right-click the icon, and select Show Package Contents
6. In that window, navigate to “Contents/MacOS”
7. Rename “firefox-bin” to “firefox-bin1”.
8. Create a new text file, and paste in this code:

   /Applications/Firefox.app/Contents/MacOS/firefox-bin1 -P ProfileName &

   *ProfileName should be the name of the profile you created in the Profile Manager.

9. Save the file as “/Applications/Firefox.app/Contents/MacOS/firefox-bin” (no extension).
10. Run this command in the Terminal:

    chmod +x /Applications/Firefox.app/Contents/MacOS/firefox-bin

11. Congratulations! You should be able to run multiple instances of Firefox.