So it seems like Firefox 67 will implement a new "Feature" to "Protect users from running old versions of Firefox". Nice try Mozilla.
~15% of Firefox users are sticking with version 56 or earlier.
By the nature of its design Coldfox should natively stop 67 from interfering with your old install but I will check this before release. Firefox 67 is due out on the 14th and I expect to have Coldfox 67 out by the 16th. Not that there will be significantly more features and from the looks of it most people will be fine sticking with 66 until 68 comes out.