Failing sometimes tests with FF55

[Paxa]

It works fine in CI: https://travis-ci.org/Paxa/slimerjs/jobs/268888244
But when I run it with docker for mac:

2017-08-27T12:12:01.357Z [DEBUG] network: request ignored: http://www.tamasoft.co.jp/en/general-info/general-info.css flags:TRANSFERRING,IS_REQ,
2017-08-27T12:12:01.357Z [DEBUG] network: progress total:19901/1203896; uri: 431/19901 for http://www.tamasoft.co.jp/en/general-info/general-info.css
2017-08-27T12:12:01.366Z [DEBUG] network: resource #2 response end status: http://www.tamasoft.co.jp/en/general-info/general-info.css
2017-08-27T12:12:01.367Z [DEBUG] network: request ignored: http://www.tamasoft.co.jp/en/general-info/general-info.css flags:STOP,IS_REQ,
2017-08-27T12:12:01.367Z [DEBUG] network: status change for http://www.tamasoft.co.jp/en/general-info/unicode.html (2152398854): Transferring data from www.tamasoft.co.jp…
JavaScript strict warning: http://www.tamasoft.co.jp/en/general-info/unicode.html, line 57: ReferenceError: assignment to undeclared variable google_ad_client
JavaScript strict warning: http://www.tamasoft.co.jp/en/general-info/unicode.html, line 59: ReferenceError: assignment to undeclared variable google_ad_slot
JavaScript strict warning: http://www.tamasoft.co.jp/en/general-info/unicode.html, line 60: ReferenceError: assignment to undeclared variable google_ad_width
JavaScript strict warning: http://www.tamasoft.co.jp/en/general-info/unicode.html, line 61: ReferenceError: assignment to undeclared variable google_ad_height
2017-08-27T12:12:01.414Z [DEBUG] network: status change for http://www.tamasoft.co.jp/en/general-info/unicode.html (2152398854): Transferring data from www.tamasoft.co.jp…
2017-08-27T12:12:01.414Z [DEBUG] network: progress total:21877/1203896; uri: 21446/21877 for http://www.tamasoft.co.jp/en/general-info/unicode.html
2017-08-27T12:12:01.416Z [DEBUG] network: request ignored: http://pagead2.googlesyndication.com/pagead/show_ads.js flags:START,IS_REQ,
2017-08-27T12:12:01.417Z [DEBUG] network: resource request #3 started: GET - http://pagead2.googlesyndication.com/pagead/show_ads.js flags=
/usr/bin/firefox: line 3:    82 Segmentation fault      DISPLAY=:0.0 /opt/firefox/firefox $@

ran few times, always same result

is it a bug or just a edge case with my setup?