MuseScore is a powerful and widely used open-source music notation software. Mac users often appreciate its extensive features and cross-platform capabilities, but one common issue can interrupt the workflow—multiple copies of MuseScore sometimes appear to run simultaneously or launch in separate instances, cluttering the workspace and system memory. If you’re a macOS user looking to streamline your MuseScore experience and ensure that it always opens as a single application instance, you’re not alone. This article will guide you through solving this problem, explaining why it happens and walking you through simple steps to prevent it.

TL;DR

If MuseScore is opening in multiple instances or separate windows on macOS, it is likely due to how macOS handles application bundles and system file associations. To resolve this, ensure that MuseScore is installed correctly in the Applications folder, avoid launching from multiple duplicates or disk images, and use the terminal or system preferences to set preferred behaviors. Below are detailed steps and best practices to make MuseScore run as a single, unified application every time you open it.

Understanding the Problem

Before jumping into the solution, it’s important to understand why MuseScore might seem to open in multiple instances on your Mac.

• Multiple installs: You may have unintentionally installed more than one copy of MuseScore.
• Opening via disk image (.dmg): Running the app from the disk image rather than the Applications folder creates a temporary instance.
• File association errors: macOS might try to open scores with different versions of MuseScore if file type associations aren’t set correctly.
• Misuse of “Open With”: Launching files directly via right-click without proper default settings can spawn multiple app instances.

Step-by-Step Solutions

1. Verify Installation in the Applications Folder

macOS best practices recommend installing all trusted applications in the main Applications folder.

Follow these steps:

1. Open the Finder.
2. Navigate to the location where MuseScore was downloaded (most likely your Downloads folder).
3. Check if you’re running MuseScore from inside a .dmg file. If so, close MuseScore.
4. Drag and drop the MuseScore app into the Applications folder.
5. Open it once from the Applications folder to ensure correct installation.

Once MuseScore is placed correctly, always launch it from the Applications folder or your Dock (after dragging it there). Avoid launching it directly from the .dmg file.

2. Remove Duplicate Versions

Multiple installs can confuse macOS into launching multiple instances. Do a thorough check to ensure only one copy exists.

To remove duplicates:

1. Open Spotlight by pressing Cmd + Space and type “MuseScore”.
2. Note where the app launches from. If more than one path shows up, you likely have duplicates.
3. Use Finder to locate all copies of MuseScore on your system.
4. Move any old, extra copies to the Trash and empty it.

After this, restart your Mac to clear any running processes that might refer to the duplicate copies.

3. Set MuseScore as the Default App for Score Files

macOS uses “Default Application” settings to decide which app to use when opening files. If you have multiple MuseScore versions, this can lead to file conflicts.

Here’s how to fix it:

1. Find a MuseScore file (with the .mscz extension).
2. Right-click the file and select Get Info.
3. Under the section Open with:, choose the correct MuseScore app (the one in your Applications folder).
4. Click Change All… to make it the default app for all MuseScore files.

This ensures all MuseScore files open with a single, consistent app instance from now on.

4. Use Terminal to Check for Running Instances

macOS sometimes doesn’t show all background app processes in the Dock. Use Terminal to check what’s really running.

To do this:

1. Open the Terminal app (found under Applications > Utilities).
2. Type the following command and press Enter:

ps aux | grep MuseScore

This will list all running processes related to MuseScore. If multiple instances show up, kill them manually using their Process ID (PID):

kill <PID>

Example:

kill 2849

Once all extra instances are closed, relaunch MuseScore from the Applications folder.

5. Avoid Launching via Recent Files or External Drives

If you’ve been using MuseScore files from an external USB, shared network drive, or downloaded folder, macOS might reference older versions stored there.

Best practices include:

• Always save and open your scores from a local drive, ideally your Documents or Music folder.
• Do not run MuseScore from Time Machine backups or external installations.
• If using Muse Hub, ensure it’s correctly linked to the Applications version of MuseScore.

6. Reinstall MuseScore When in Doubt

If the issue persists even after performing the above steps, a clean reinstall may be your best option.

Reinstall MuseScore by:

1. Going to the Applications folder and moving MuseScore to the Trash.
2. Emptying the Trash to completely remove the app.
3. Visiting the official MuseScore website and downloading the latest macOS version.
4. Installing it into the Applications folder as previously mentioned.

This method removes any misconfigurations and ensures you’re starting from a clean slate.

Advanced Users: Use AppleScript to Force Single Instance

More advanced users may want to wrap MuseScore with a short AppleScript that ensures only one instance runs.

Sample script:

tell application "System Events"
  if (count of (every process whose name is "MuseScore 4")) = 0 then
    tell application "MuseScore 4" to activate
  end if
end tell

You can save this script as an app via the Script Editor and launch MuseScore through it to ensure single-launch behavior.

Final Checks and Best Practices

• Pin MuseScore to your Dock once you’re sure you’re using the correct version.
• Avoid opening MuseScore by dragging files onto the app icon unless necessary.
• Disable open-at-login for any duplicate versions that may have snuck into your startup items.
• Regularly clean Downloads and disk images to avoid re-launching from them mistakenly.

Conclusion

MuseScore is an excellent tool, but like many intricate applications, it can misbehave if not properly installed or managed—especially on macOS where users often tinker with drag-and-drop installations or launch files in unconventional ways. The key takeaway here is to ensure that you have one clean installation in your Applications folder, with proper file associations and no background duplicates running.

With just a little attention to setup and launch behavior, you can ensure MuseScore opens as a single app every time—making your music-writing experience smoother, faster, and more reliable.