This change is designed to fix a bug in the Firefox extension which results in some downloads not being captured by the extension.

Reproduction steps for the bug in the current version are as follows:

1. Open a new window of Firefox and make sure the Gopeed extension is installed.
2. Open two tabs, one being the Gopeed website https://gopeed.com/ and the other being the Pop Os download page https://system76.com/pop/download/.
3. Click the green Download button on the Gopeed tab (download should be captured).
4. Switch to the Pop Os tab and hit one of the yellow Download buttons (should fail to be captured and handled by the browser instead)

In order to fix this, I changed the way the download event skip tracking works by creating a Map that associates the skip status per download rather than as one global boolean.