The Block parameters for the InstallAddons policy doesn't make sense because the addons install process has two behaviors:
- Allow
- Ask

So a website that is not explictly in the allow list will always ask for permission before installing an addon. If a sysadmin wants to fully block addon install they can use a different policy.

Similarly, for Popups it's the same thing. There is a conceptually valid use case in that someone can change the _default_ behavior to always allow popups, and then the Block list becomes the allow exceptions to Ask. But that's a corner case that we don't need to support now, since allowing popups globally on the web is a pretty crazy choice.

MozReview-Commit-ID: EzclfLNDgUo

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extra : rebase_source : 37753de1bad9c09ea89f537f1a80f4eed5494def