Add NodeFirefoxNightly image (#470)

* use same Firefox image for nightly

Author: smccarthy

NodeFirefox/Dockerfile.txt

@@ -4,10 +4,11 @@ USER root
 # Firefox
 #=========
 ARG FIREFOX_VERSION=57.0.4
-RUN apt-get update -qqy \
+RUN FIREFOX_DOWNLOAD_URL=$(if [ $FIREFOX_VERSION = "nightly" ]; then echo "https://download.mozilla.org/?product=firefox-nightly-latest-ssl&os=linux64&lang=en-US"; else echo "https://download-installer.cdn.mozilla.net/pub/firefox/releases/$FIREFOX_VERSION/linux-x86_64/en-US/firefox-$FIREFOX_VERSION.tar.bz2"; fi) \
+  && apt-get update -qqy \
   && apt-get -qqy --no-install-recommends install firefox \
   && rm -rf /var/lib/apt/lists/* /var/cache/apt/* \
-  && wget --no-verbose -O /tmp/firefox.tar.bz2 https://download-installer.cdn.mozilla.net/pub/firefox/releases/$FIREFOX_VERSION/linux-x86_64/en-US/firefox-$FIREFOX_VERSION.tar.bz2 \
+  && wget --no-verbose -O /tmp/firefox.tar.bz2 $FIREFOX_DOWNLOAD_URL \
   && apt-get -y purge firefox \
   && rm -rf /opt/firefox \
   && tar -C /opt -xjf /tmp/firefox.tar.bz2 \
@@ -43,5 +44,3 @@ RUN sudo echo ""
 
 # Generating a default config during build time
 RUN /opt/bin/generate_config > /opt/selenium/config.json
-
-