Please rewrite this URL to remove the /z/: https://addons-dev.allizom.org/z/en-US/admin/addon-search This is on dev+stage. I'll add it to the etherpad for prod. We'll probably have a bunch more /admin/* URLs in the future, so you might want to make the rewrite friendly for that kind of thing.
RewriteRule ^((?:/[^/]+)?/admin/addon-search(?:/.*)?) /z$1 [PT]