This was verified to work on Ubuntu 16.10 with Firefox 52.0a2 developer edition (15 Apr 17).
Super simple:
- Follow the instructions on the Ubuntu community wiki: https://help.ubuntu.com/community/CommonAccessCard
- Install cackey from this repository
- This is the package from Forge.mil, included here for ease of installation since Forge.mil requires a working CAC to download
- If you have trouble installing the DEB via dpkg, open it with archive manager and extract the data.tar.gz file, then copy libcackey.so to the /usr/lib directory.
- Configure Firefox by going to Preferences -> Advanced -> Security Devices then selecting Load and point it to the libcackey.so file.