How to Run Firefox Nightly and Quantum Side-by-Side with Separate Profiles

Firefox Nightly lets you experience cutting-edge features in development—some that may never reach stable releases. However, running it alongside Firefox Quantum (the stable version) poses risks, as both share the same profile by default. Nightly's experimental nature increases the chance of profile corruption.

Additionally, you can't run both browsers simultaneously without tweaks, which is problematic for tasks needing stability alongside testing.

Luckily, creating separate profiles resolves this. With Firefox Sync, you can keep bookmarks, passwords, and history consistent across them. Here's how, based on years of hands-on Firefox customization.

Also read: How to Disable Pocket for Firefox on Desktop and Mobile

Create separate profiles

The Firefox Profile Manager makes this straightforward. Since Nightly and Quantum are distinct installs, we'll modify their shortcuts too.

Important: Fully close both browsers first. Print these steps or use another browser like Chrome or Edge.

Step 1: Press Windows + R, enter firefox -p, and hit OK.

Step 2: In Profile Manager, note the default profile—reserve it for Quantum.

Click Create Profile... for Nightly.

Step 3: Name it Nightly (or similar) and click Finish.

Step 4: Click Exit.

Next, update shortcuts. Install Nightly if needed.

Step 5: Right-click the Nightly desktop shortcut > Properties.

Step 6: On the Shortcut tab, append -p Nightly to the Target (one space). Use quotes for multi-word names, e.g., -p "FF Nightly".

Important: Maintain one space before the parameter.

Click Apply > OK.

Step 7: Repeat for Quantum, using -p default (or omit if default).

Switch freely without corruption risks.

Step 8: Sync data via Firefox Sync: Menu > Sign in to Sync in each browser.

Note: Create a Firefox Account if needed.

This syncs across profiles but doesn't enable simultaneous use yet.

Also read: 15 Best Firefox Addons You Should Be Using

Run both browsers simultaneously

By default, launching one blocks the other. Fix it by editing the Nightly shortcut again.

Right-click Nightly shortcut > Properties. Append --no-remote to Target (keep prior parameters).

Save changes. Now run both independently—Sync continues working.

Note: Nightly's instability may cause crashes or affect Quantum.Also read: 6 reasons why you should give Firefox Quantum a shot

You're all set!

Enjoy stable Quantum and experimental Nightly without issues. Use Sync for seamless data access, and run them side-by-side for ultimate flexibility.

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