The binary package purebrowser was previously packaged from source package purebrowser.
To minimize delta towards Debian, and ease tracking differences, binary package purebrowser is now packaged from source package firefox-esr.
Please therefore lift the ban of source package firefox-esr.
NB! There should be a PureOS release of src:firefox-esr already uploaded. If that is not the case, then tell how to prepare differently, so as to avoid temporarily letting through Debian firefox-esr package!