To find the APK App Purchase File)for 科学上网firefly,you can follow these steps:

1. Visit Official Platforms: Check the official website of "科学上网firefly" or any related discussion forums where users might share app binaries. For example, websites like Steam, Reddit, or gaming communities could have the APK.

2. Search on Google: Use Google or Bing to search for "科学上网firefly APK." This might bring up links to the APK file.

3. GitHub or Code Platforms: If the app is peer-reviewed or developed by a company, visit their GitHub repository or other code platforms to check for the APK file.

4. Community Forums: Engage with the community or gaming forums where the app is popular. Many users share their APKs there.

5. Developer Support: If you're unable to find the APK through the above methods, consider reaching out to the developers directly. Many developers provide access to their code and APKs upon request.

6. Legal Considerations: Ensure that you are accessing the APK through legitimate channels and not infringing on any intellectual property rights.

If you provide more details about the app, such as its purpose or where it's used, I might be able to give you more specific guidance.