conkeror-https-everywhere software package provides virtual package provided by xul-ext-https-everywhere, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install conkeror-https-everywhere
conkeror-https-everywhere is installed in your system.
Make ensure the conkeror-https-everywhere package were installed using the commands given below,
$ sudo dpkg-query -l | grep conkeror-https-everywhere*
You will get with conkeror-https-everywhere package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Virtual packages |
| Package | conkeror-https-everywhere |
| Version | |
| Description | virtual package provided by xul-ext-https-everywhere |
| Sub Section | Virtual |