Firefox port issue

[Walter Schwarzenfeld]

I don't believe this causss the error, but your syntax is deprecated, use:

DEFAULT_VERSIONS+=linux=c7_64 ruby=ruby?.2 python=2.7 ssl=openss bdb=6l

in one line.

If you have other versions of python installed you need e.g.
python=2.7 python2=2.7 python3=3.5 in DEFAULT_VERSIONS.