This is intentional to focus the details page more and simplify.
For collections users still can add add-ons in the collections section of AMO.
I am not sure if those feature are used enough to justify the prominent placement.

Sounds like this is working as expected, so I'll close this as "by design"; feel free to reopen if I'm mistaken.

If you do not use collections, then I think you are missing the significance of what removing the 2 "simple" links does (Add to Favorites and Add to Collection). It has made it EXTREMELY difficult to manage collections without them. I think it is a great lack of appreciation of how useful collections are and the way they need to be accessed (by collection creators/managers).

Also, given the amount of info on the pages anyway, 2 links on this page are not going to make a UI difference BUT they do add HUGE value.

Please see my 3 comments here:
https://discourse.mozilla-community.org/t/no-favorite-button-in-new-amo-design/8015/12?u=smayer97

https://discourse.mozilla-community.org/t/no-favorite-button-in-new-amo-design/8015/13?u=smayer97

https://discourse.mozilla-community.org/t/no-favorite-button-in-new-amo-design/8015/14?u=smayer97

Please seriously reconsider this. Please do not alienate users of collections.

@smayer97 Really stupid, I was thinking it was an error but it's an HORROR!

Wow reality surpass fiction !

Mozarella is going deep in the Dumb Browser Game, with this move they are clearly the leader for the in that field. :(

I really hope Vivaldi will improve a little bit and add sync system soon this way I will run away with my userscripts and userstyles.

Here's a fix with a Userstyle that improve a lot AMO and make it usable at least: https://userstyles.org/styles/126536/amo-ez-on-the-eyes

Just re-add the damn button, is it so hard to do?

This is a duplicate of #2876, which is open. Looks like the plan is to add back to "Add to favourites" button.

I'm locking this issue; there's no need for swearing or name-calling.