There is no way for a user to know what all domains can an extension access data from if the host permissions >= 4.
Consider this extension https://addons.mozilla.org/en-US/firefox/addon/google-search-result-shortcuts
It says it can access data from google.com, google.ad, google.ae and 190 other domains - This information is kind of really insufficient and vague for a user.
I am sure we dont want to put all 190 domains in product page, but may be a popup or see more kind of stuff may help.

That's a good question. It could be a nice improvement to inform end users. /cc @jvillalobos @pwalm
There might be a dupe of this one somewhere, because I know we've talked about it before. The current display is consistent with Firefox, and I think it's fine as a default.
Having a secondary exhaustive list sounds like a good idea, but it would need to account for an arbitrary number of permissions. If we get the UX for it, I'm for doing it.
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@mirefly wanna give it a try? :D
Reopening this one because FF has been fixed to display all the permissions/domains.
@willdurand Yeah, I am gonna have a try.
@willdurand Listing all permission will push some cards ("Release note" and "Add to collection") to the very end of the page when there are many domain names. It looks not good. Do we want to simply list all permissions, or just show the "other host/site names" as tooltip text when mouse over the text "Access your data in ** other domains" (or other suggestions)?
could we use a ShowMoreCard?
Verified fixed on stage.
Before:

After:

This is the add-on example from stage: https://addons.allizom.org/en-US/firefox/addon/many-domain-perms/
All the given domains are now visible on the detail page by expanding the Permissions card (clicking Read more)
Most helpful comment
There might be a dupe of this one somewhere, because I know we've talked about it before. The current display is consistent with Firefox, and I think it's fine as a default.
Having a secondary exhaustive list sounds like a good idea, but it would need to account for an arbitrary number of permissions. If we get the UX for it, I'm for doing it.