I know this feature under the name “APT pinning”.
My understanding is that APT pinning works by referencing certain fields of a Release/InRelease file in the configured repository. In your case you are setting a Pin-Priority of 1001 for the Release file that has the line Origin: LP-PPA-mozillateam in it.
The problem is that Katello publishes APT repos in a different structure than the original upstream repository. Which means there may no longer be a Release file with the line Origin: LP-PPA-mozillateam in it.
We are working on having Katello mirror the same repo structure as the original upstream repos, but that is more of a long term effort, see: RFC: Transitioning Katello to "structured APT (deb) content"
In the mean time, you might be able to achieve the result you want, by creating content views with filters to filter out the packages you don’t want used from one repo, to force it to be used from the repo you do want it used from instead. Then you would no longer need APT pinning on your clients.