diff --git a/src/flask/app_factory.py b/src/flask/app_factory.py
index 348dbd6..5e40a69 100644
--- a/src/flask/app_factory.py
+++ b/src/flask/app_factory.py
@@ -97,6 +97,19 @@ def create_app(config: dict | None = None) -> Flask:
         if response.mimetype == "text/html":
             response.headers["Cache-Control"] = "no-store, must-revalidate"
             response.headers["Pragma"] = "no-cache"
+        elif response.mimetype in ("text/css", "application/javascript",
+                                    "text/javascript"):
+            # The static files must NEVER be reused from a cache.
+
+            # Firefox kept serving a stale stylesheet even with
+            # `no-cache`, which meant the page had the new markup and
+            # the old CSS: the advice was expanded inline in the table
+            # instead of in a pop-out, and the long and short labels
+            # were both showing ("BREWING ADVICEADVICE").
+
+            # `no-store` is the only one that means "do not keep this".
+            response.headers["Cache-Control"] = "no-store, must-revalidate"
+            response.headers["Pragma"] = "no-cache"
         return response
 
     csrf = CSRFProtect(app)
diff --git a/src/flask/static/css/app.css b/src/flask/static/css/app.css
index 11dd675..9f5c882 100644
--- a/src/flask/static/css/app.css
+++ b/src/flask/static/css/app.css
@@ -999,10 +999,21 @@ table.data .comment { color: var(--text-muted); font-size: .84rem; }
 
 /* The script opens and closes the panel, and places it.  The CSS only
    decides whether it is shown. */
+/* The panel is opened by the script, which removes the `hidden`
+   attribute and adds `is-open`.
+
+   The `hidden` attribute is what makes this fail-safe: if the
+   stylesheet is stale and does not know about `.advice-pop` at all,
+   the panel is STILL hidden, so the advice cannot appear expanded
+   inside the table cell. */
 .advice-pop.is-open {
     display: block;
 }
 
+.advice-pop[hidden] {
+    display: none;
+}
+
 /* On a phone there is no hover, so the trigger is a button the script
    toggles, and the panel is pinned to the middle of the screen so it is
    readable whatever the table's width. */
diff --git a/src/flask/static/js/app.js b/src/flask/static/js/app.js
index a8b0400..6c6b6d4 100644
--- a/src/flask/static/js/app.js
+++ b/src/flask/static/js/app.js
@@ -131,6 +131,11 @@
                         clearTimeout(closeTimer);
                         closeTimer = null;
                     }
+                    /* The `hidden` attribute is removed as well as the
+                       class added, so the panel is shown even if the
+                       stylesheet is an older one that only knows about
+                       the class. */
+                    panel.removeAttribute("hidden");
                     panel.classList.add("is-open");
                     trigger.setAttribute("aria-expanded", "true");
                     place();
@@ -138,6 +143,9 @@
 
                 function close() {
                     panel.classList.remove("is-open");
+                    /* Put the attribute back, so a stale stylesheet
+                       cannot leave the advice expanded in the cell. */
+                    panel.setAttribute("hidden", "");
                     trigger.setAttribute("aria-expanded", "false");
                 }
 
diff --git a/src/flask/templates/brews.html b/src/flask/templates/brews.html
index 7640b8a..b165c9a 100644
--- a/src/flask/templates/brews.html
+++ b/src/flask/templates/brews.html
@@ -126,7 +126,7 @@
                                                 {% endif %}
                                             </span>
                                         </button>
-                                        <div class="advice-pop" role="tooltip">
+                                        <div class="advice-pop" role="tooltip" hidden>
                                             <div class="advice-pop__head">
                                                 <span class="advice__label">Brewing advice</span>
                                                 <button type="button" class="advice-pop__close"
diff --git a/tests/test_brew_advice.py b/tests/test_brew_advice.py
index 6b50828..4d2a52e 100644
--- a/tests/test_brew_advice.py
+++ b/tests/test_brew_advice.py
@@ -1162,6 +1162,29 @@ def test_stale_advice_cannot_overwrite_a_comment_edited_outside_the_app(repo):
     assert doc["comment"] == "edited outside the app"
 
 
+def test_the_advice_pop_out_is_hidden_in_the_markup(client, repo):
+    """The pop-out carries the `hidden` attribute.
+
+    A stale stylesheet - one that does not know about `.advice-pop` at
+    all - would otherwise leave the advice expanded inline in the table
+    cell, running down the column and off the screen.  The `hidden`
+    attribute makes the markup fail-safe: the panel stays hidden until
+    the script opens it.
+    """
+    repo.users.insert_one({"username": "beer", "password": "beer_pass"})
+    client.post("/login", data={"username": "beer", "password": "beer_pass"},
+                follow_redirects=True)
+
+    seed_readings(repo, [("1", "Ale", "1042", "2026-01-01", False, "")])
+    doc = repo.readings.find_one({"beer_run_id": "1"})
+    repo.set_reading_advice(str(doc["_id"]), "Warm it to 21C and wait.", ok=True)
+
+    body = client.get("/brews").get_data(as_text=True)
+
+    assert 'class="advice-pop"' in body
+    assert 'hidden' in body.split('class="advice-pop"')[1][:60]
+
+
 def test_a_failed_advice_is_marked_as_such(client, repo):
     """A generation failure reads differently from real advice."""
     repo.users.insert_one({"username": "beer", "password": "beer_pass"})