- Find release date of desired Safari version looking at the wiki page. Safari 6.1.6 was released around August, 2014.
- Find a version of the epiphany-browser package from a similar date by browsing the debian package history If you click on the links there it'll show the date the package appeared. epiphany-browser 3.12.1-1 is from around July, 2014.
- Look in the Ubuntu history of the epiphany package to see if there's an Ubuntu release that has a version close to what you want. I'm currently running Bionic, and saw the Trusty has a close version, 3.10.3-0ubuntu2.
- Add the old Trusty repository to your /etc/apt/sources.list by adding the following lines:
deb http://us.archive.ubuntu.com/ubuntu trusty universe deb http://us.archive.ubuntu.com/ubuntu trusty multiverse deb http://security.ubuntu.com/ubuntu trusty-security main deb http://cz.archive.ubuntu.com/ubuntu trusty main
- The run some apt command to update and get the correct version. I found the right packages to include by trial and error as the apt-get install command would fail:
My guess is that it's not a good idea to leave the trusty source lines in sources.list long-term since it might confuse future upgrades and may also confuse apt-cache. I plan to remove and try to cleanup once I'm done testing.