Prepare the game itself
Visit the official ORBIT website and follow Play. The game and the information website use different addresses, so reading a guide is not a substitute for opening the playable game. If you plan to use a Home Screen icon, launch that icon online as part of preparation.
ORBIT begins registering its offline service worker after the page loads. Keep the connection available while the browser retrieves the game files. Starting a run immediately proves that the page is usable now; it does not prove that the offline setup has finished.
Check the result in the intended context
The game’s installation help can show Ready for offline play when its service worker becomes ready. Where that help is available, use the status as a useful signal. The stronger practical check is to reopen the game with connectivity disabled.
Test from the same icon or browser context you intend to use later. Start a short run, inspect the forest and try your preferred sound settings. Testing only a page that remained open can miss a problem with launching after the page has closed.
Keep expectations specific
The offline shell is designed for the game. External websites, email support and sending a challenge through another service still depend on those services and your connection. Audio also needs its own test because the fallback audio format is not included in the precached shell.
If the offline launch fails, reconnect and revisit the game before trying again. Avoid clearing site data as a setup shortcut: that can remove local progress as well as offline files. An installed icon is convenient, but it cannot guarantee files remain stored forever.