Use Chrome PPA, update chromedriver, firefox

* No need to download our specific version
* Use officially supplied FF 45

playbooks/roles/browsers/defaults/main.yml

 browser_deb_pkgs:
-    - xvfb
     - dbus-x11
+    - firefox
+    - gdebi
+    - libcurl3
     - libgconf2-4
-    - libxss1
     - libnss3-1d
-    - libcurl3
+    - libxss1
     - xdg-utils
-    - gdebi
+    - xvfb
 
 # Debian packages we host in S3 to ensure correct browser version
 # Both Chrome and FireFox update their apt repos with the latest version,
 # which often causes spurious acceptance test failures.
 browser_s3_deb_pkgs:
-    - { name: "firefox-mozilla-build_42.0-0ubuntu1_amd64.deb", url: "https://s3.amazonaws.com/vagrant.testeng.edx.org/firefox-mozilla-build_42.0-0ubuntu1_amd64.deb" }
     - { name: "google-chrome-stable_55.0.2883.87-1_amd64.deb", url: "https://s3.amazonaws.com/vagrant.testeng.edx.org/google-chrome-stable_55.0.2883.87-1_amd64.deb" }
 
+# Firefox
+firefox_version: version 45.*
+
 # ChromeDriver
 chromedriver_version: 2.27
 chromedriver_url: "http://chromedriver.storage.googleapis.com/{{ chromedriver_version }}/chromedriver_linux64.zip"

playbooks/roles/browsers/tasks/main.yml

 # Install browsers required to run the JavaScript
 # and acceptance test suite locally without a display
 ---
+- name: lock Firefox version
+  copy:
+    dest: /etc/apt/preferences.d/firefox-pinned-version
+    content: |
+      Package: firefox
+      Pin: {{ firefox_version }}
+      Pin-Priority: 1001
+  tags:
+    - install
+    - install:system-requirements
+
 - name: install system packages
-  apt: pkg={{','.join(browser_deb_pkgs)}}
-       state=present update_cache=yes
+  apt:
+    pkg: "{{ ','.join(browser_deb_pkgs) }}"
+    update_cache: yes
+  tags:
+    - install
+    - install:system-requirements
 
 - name: download browser debian packages from S3
   get_url: dest="/tmp/{{ item.name }}" url="{{ item.url }}"
   register: download_deb
   with_items: "{{ browser_s3_deb_pkgs }}"
+  tags:
+    - install
+    - install:system-requirements
 
 - name: install browser debian packages
   shell: gdebi -nq /tmp/{{ item.name }}
   when: download_deb.changed
   with_items: "{{ browser_s3_deb_pkgs }}"
+  tags:
+    - install
+    - install:system-requirements
 
 # Because the source location has been deprecated, we need to
 # ensure it does not interfere with subsequent apt commands
@@ -21,55 +42,97 @@
   file:
     path: /etc/apt/sources.list.d/google-chrome.list
     state: absent
+  tags:
+    - install
+    - install:system-requirements
 
 - name: download ChromeDriver
   get_url:
-    url={{ chromedriver_url }}
-    dest=/var/tmp/chromedriver_{{ chromedriver_version }}.zip
+    url: "{{ chromedriver_url }}"
+    dest: /var/tmp/chromedriver_{{ chromedriver_version }}.zip
   register: download_chromedriver
+  tags:
+    - install
+    - install:system-requirements
 
 - name: unzip ChromeDriver tarfile
   shell: unzip /var/tmp/chromedriver_{{ chromedriver_version }}.zip
-         chdir=/var/tmp
+  args:
+    chdir: /var/tmp
   when: download_chromedriver.changed
+  tags:
+    - install
+    - install:system-requirements
 
 - name: move ChromeDriver binary to /usr/local
   shell: mv /var/tmp/chromedriver /usr/local/bin/chromedriver
   when: download_chromedriver.changed
+  tags:
+    - install
+    - install:system-requirements
 
 - name: make ChromeDriver binary executable
-  file: path=/usr/local/bin/chromedriver mode=0755
+  file:
+    path: /usr/local/bin/chromedriver
+    mode: 0755
   when: download_chromedriver.changed
+  tags:
+    - install
+    - install:system-requirements
 
 - name: verify ChromeDriver location and mode
-  stat: path=/usr/local/bin/chromedriver
+  stat:
+    path: /usr/local/bin/chromedriver
   register: chromedriver
+  tags:
+    - install
+    - install:system-requirements
+
 - assert:
     that:
       - "chromedriver.stat.exists"
       - "chromedriver.stat.mode == '0755'"
+  tags:
+    - install
+    - install:system-requirements
 
 - name: download PhantomJS
   get_url:
     url: "{{ phantomjs_url }}"
     dest: "/var/tmp/{{ phantomjs_tarfile }}"
   register: download_phantom_js
+  tags:
+    - install
+    - install:system-requirements
 
 - name: unpack the PhantomJS tarfile
   shell: "tar -xjf /var/tmp/{{ phantomjs_tarfile }}"
   args:
     chdir: "/var/tmp"
   when: download_phantom_js.changed
+  tags:
+    - install
+    - install:system-requirements
 
 - name: move PhantomJS binary to /usr/local
   shell: mv /var/tmp/{{ phantomjs_version }}/bin/phantomjs /usr/local/bin/phantomjs
   when: download_phantom_js.changed
+  tags:
+    - install
+    - install:system-requirements
 
 - name: verify phantomjs location
   stat: path=/usr/local/bin/phantomjs
   register: phantomjs
+  tags:
+    - install
+    - install:system-requirements
+
 - assert:
     that: "phantomjs.stat.exists"
+  tags:
+    - install
+    - install:system-requirements
 
 - name: create xvfb upstart script for Precise and Trusty (12.04 and 14.04)
   template:
@@ -77,7 +140,7 @@
     dest: /etc/init/xvfb.conf
     owner: root
     group: root
-  when: ansible_distribution_release == 'precise' or ansible_distribution_release == 'trusty'
+  when: ansible_distribution_release in ['precise', 'trusty']
   tags:
     - install
     - install:configuration
@@ -85,7 +148,7 @@
 - name: start xvfb upstart script for Precise and Trusty (12.04 and 14.04)
   shell: start xvfb
   ignore_errors: yes
-  when: ansible_distribution_release == 'precise' or ansible_distribution_release == 'trusty'
+  when: ansible_distribution_release in ['precise', 'trusty']
   tags:
     - install
     - install:configuration