Do pages opened from different files share saved data?

Press the button. Then save this same page a second time (under another name, or in another folder), open that copy, and press its button too. Each copy tells you what it can see of the other. Pressing the button again in the same copy is fine.

Run the check

Nothing leaves this device. The check writes one small entry to this browser's saved data (key storage-probe:v1, plus a test key that is removed at once); clear it by clearing the site data for this page.