Building a Chrome extension that saves items from arbitrary third-party sites means every site is a hostile, unstable environment. Here is what actually broke, and what held.

Manifest V3 changes the shape of everything

The persistent background page is gone. Service workers terminate — aggressively, after roughly 30 seconds of inactivity — and any in-memory state dies with them.

Anything that must survive goes into chrome.storage:

// ❌ dies with the worker