First version

firefox.yml

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+- name: Firefox (home page and bookmarks of the contest)
+  hosts: all
+  become: yes
+  vars:
+    contest_url: https://atlantic-canada26.kattis.com
+    contest_id: atlantic-canada26
+    policies: /usr/lib/firefox/distribution/policies.json
+    # The bookmarks of the ICPC image point to http://contest, which is the
+    # contest server of the World Finals. They are replaced by the Kattis pages.
+    bookmarks:
+      - { Placement: toolbar, Title: "Contest", URL: "{{ contest_url }}/contests/{{ contest_id }}" }
+      - { Placement: toolbar, Title: "Problems", URL: "{{ contest_url }}/contests/{{ contest_id }}/problems" }
+      - { Placement: toolbar, Title: "Standings", URL: "{{ contest_url }}/contests/{{ contest_id }}/standings" }
+      - { Placement: toolbar, Title: "Contest Help (offline)", URL: "file:///usr/share/doc/acpc/help/index.html" }
+      - { Placement: toolbar, Title: "Language Documentation", URL: "https://devdocs/" }
+      - { Placement: toolbar, Title: "Technical Notes", URL: "file:///usr/share/doc/icpc/TechNotes.pdf" }
+
+  tasks:
+    - name: Set the home page and the bookmarks
+      shell: |
+        python3 - "{{ policies }}" <<'PY'
+        import json, sys
+        path = sys.argv[1]
+        data = json.load(open(path))
+        p = data.setdefault("policies", {})
+        before = json.dumps(data, sort_keys=True)
+        p["Bookmarks"] = json.loads('{{ bookmarks | to_json }}')
+        p["Homepage"] = {"Locked": True, "StartPage": "homepage-locked",
+                         "URL": "{{ contest_url }}"}
+        # No extensions can be installed, and about:config is closed
+        p["ExtensionSettings"] = {"*": {"installation_mode": "blocked"}}
+        p["BlockAboutConfig"] = True
+        if json.dumps(data, sort_keys=True) != before:
+            json.dump(data, open(path, "w"), indent=2)
+            print("changed")
+        PY
+      register: ff
+      changed_when: "'changed' in ff.stdout"