Incomplete or missing tracker database on install after granting Private Browsing permission in Firefox

[ghostwords]

Moments after installing Privacy Badger in Firefox, Firefox shows the Private Browsing permission "door hanger". Clicking to allow Privacy Badger to run in Private windows restarts Privacy Badger.

If you restart Privacy Badger quickly enough, you may interrupt Privacy Badger's loading of seed tracker data into memory from a local file. You may also interrupt loading of the yellowlist and EFF's DNT policy hashes, but this is less likely as these assets are small and load much quicker than seed data.

Interrupting seed data loading results in a partially broken installation where Privacy Badger has little or no tracker knowledge.

This bug was reactivated by 2ac8b01 after which the welcome page once again opens without a delay in Firefox.

This bug is technically not Firefox-specific but it is Firefox-specific in practice. Nowhere else are users presented with browser UI that has them restart the extension moments after installation.

See also #2798.