Migrate to Event Page from Background Page

[yorkxin]

Summary

Migrate to Event Page architecture to follow the latest best practices of Chrome Extensions.

As a part of QA, I'm going to run this version on my computers for a few days.

Tests

• [ ] Chrome stable (macOS)
• [ ] Firefox stable (macOS)
• [ ] Chrome stable (Windows)
• [ ] Firefox stable (Windows)

Optional:

• [ ] Chrome beta (macOS)
• [ ] Firefox beta (macOS)
• [ ] Chrome beta (Windows)
• [ ] Firefox beta (Windows)

[yorkxin]

On Firefox it seems that the context menu item disappears after some period of time (process being killed?)

[yorkxin]

Turns out Firefox does not support Event Page anyways. It doesn't make sense to deal with event page architecture. Closing this.

Manifest V3 might worth a do.