xulrunner 26.0 + slimerjs 0.9 with xulrunner dependency

Updated version of PR #22914 (inplace updates was broken because of the move to Homebrew/homebrew)

* added custom Python 2.7.3 requirement for devel and HEAD
* updated devel (stable on 10.9) to 27.0b2

see #22914 for more details