Leak me Clean me
No leak: Content script does nothing
jsonSandbox leak: storage.sync.get is called
jsonSandbox and content script sandbox is leaked (only if using a temporary add-on ID): storage.sync.get is called and the result is accessed

1. Click the above "Leak me" button to load 10 frames (with matching content script).
2. Visit about:memory
3. Click on "Measure" and search for "leaky, moz" to find all sandboxes.
   • If storage.sync.get is called, then 20 sandboxes are expected.
   • Otherwise, only 10 sandboxes are expected.
4. Click on the "Clean me" button above to remove all frames.
5. Return to about:memory, click on "Minimize memory usage" and "Measure".
6. Search for "leaky, moz" to find all sandboxes. There should not be any. However:
   • If "No leak" test was selected, then you do indeed not see any sandboxes.
   • If "jsonSandbox leak" was selected, then 10 "anonymous sandbox" (jsonSandbox) are leaked.
   • If "jsonSandbox and content script sandbox is leaked" is selected, then all 20 sandboxes are leaked.
     (this only happens if the add-on has a temporary add-on ID, remove the "applications.gecko.id" section from manifest.json).