Opening the publish panel for the first time is super slow

STR:

1. Load https://share.firefox.dev/2I3nxQv
1. Open the publish panel

Here is a profile showing the problem in a dev build: https://share.firefox.dev/32wNmzR

I can see 2 weird things:

1. We get the profile data while it should be asynchronous (with a promise). Probably it's asynchronous but we're still starting the process at that moment, and asynchronous doesn't mean parallel...
1. Why are we sanitizing something even when all checkboxes are checked? (Note this would fix the problem only in the case where we don't sanitize anything, so it's not good enough).

Reported to me by padenot.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-335)