diff --git a/docs/known-issues.md b/docs/known-issues.md
index b22c6be..6ee9474 100644
--- a/docs/known-issues.md
+++ b/docs/known-issues.md
@@ -280,19 +280,51 @@ after: panel 136px โ toolbar top 256, dialog bottom 279 (inside)
## 5. ๐ CSS/JS changes were invisible behind the browser cache
-**Symptom:** a fix to the theme did not appear until a hard refresh โ so the panel fix above looked
-like it had not worked at all.
+**Symptom:** a fix to the theme did not appear until a hard refresh โ so the panel fix in ยง4 looked
+like it had not worked at all. Reported twice, the second time with "is it because I'm on Firefox?"
-**Root cause:** Atheos serves `theme/main.min.css` and the generated `public/*.min.js|css` bundles
-from **stable URLs with no cache headers**, so nginx adds only `Last-Modified`/`ETag` and browsers
-legitimately reuse their cached copy.
+**It was not Firefox.** Verified in a real, scripted Firefox (155.0) against the live server with the
+fix applied:
-**Fix:** nginx now sends `Cache-Control: no-cache, must-revalidate` for `*.css`/`*.js`. Note this does
-**not** disable caching โ it forces **revalidation**, so normal loads still get a cheap 304 while any
-change is guaranteed to be picked up on the next load.
+```
+assets Firefox requested: theme/main.min.css?v=1790663824 <- versioned
+applied panel rule: height: auto; max-height: 58vh <- the fix
+dialog 193px | panel 138px | toolbar INSIDE | JS errors: none
+```
-**If you ever see a stale UI again:** force a reload (Ctrl/Cmd-Shift-R). That is the first thing to try
-before assuming a fix failed.
+The panel rendered correctly and the Branch toolbar sat inside the modal. Firefox behaves identically
+to Chromium here; it was simply still running the **old cached stylesheet**.
+
+**Root cause โ stable asset URLs, with nothing to bust them.** Atheos emits:
+
+```html
+
+
+```
+
+Same path before and after a change, and originally no cache headers at all. A browser therefore keeps
+its cached copy across an update, and never even asks the server. Changing the CSS on the server
+cannot fix that โ the browser is not fetching it.
+
+**Fix (two parts):**
+
+1. **nginx** sends `Cache-Control: no-cache, must-revalidate` for `*.css`/`*.js`. This does **not**
+ disable caching โ it forces **revalidation**, so normal loads still get a cheap 304 while changes
+ are picked up.
+2. **Versioned URLs.** `SourceManager::getTag()` and the theme link in `index.php` now append the
+ file's mtime (`?v=`). A changed file gets a **new URL** so it is fetched immediately; an
+ unchanged file keeps its URL and stays cached.
+
+Part 2 is the one that actually mattered here: it works **even against an already-poisoned cache**,
+which part 1 alone cannot do. Once the *page* refreshes (it is served `no-store`), every asset URL it
+references is new, so the stale CSS is bypassed with no manual clearing.
+
+**If you ever see a stale UI again:** force a reload (Ctrl/Cmd-Shift-R). If that fixes it, this
+section is why.
+
+**Forcing this one time:** if a browser holds an old copy, any of these work โ
+Ctrl/Cmd-Shift-R, `about:blank` then back, a private window, or `rm -rf` the profile's cache. Or just
+change the file's mtime (`touch`) and the URL changes by itself.
---
diff --git a/scripts/build-and-test.sh b/scripts/build-and-test.sh
index 21ffe68..f59ebb0 100644
--- a/scripts/build-and-test.sh
+++ b/scripts/build-and-test.sh
@@ -130,6 +130,20 @@ else
fi
echo
echo "=============================================================="
+echo "REGRESSION: asset URLs are versioned (cache-busting)"
+echo "=============================================================="
+# Stable asset URLs with no version are why a CSS/JS fix stayed invisible behind the browser cache,
+# in every browser incl. Firefox. docs/known-issues.md ยง5.
+ASSETS=$(wget -qO /tmp/bt_page.html --header='Host: 127.0.0.1' http://127.0.0.1/ 2>/dev/null; grep -oE '(href|src)="[^"]+\.(css|js)"' /tmp/bt_page.html 2>/dev/null | wc -l | tr -d ' ')
+VER=$(grep -oE '(href|src)="[^"]+\.(css|js)\?v=[0-9]+"' /tmp/bt_page.html 2>/dev/null | wc -l | tr -d ' ')
+if [ "${VER:-0}" -ge 4 ]; then
+ ok "asset URLs are versioned ($VER asset tags carry ?v=)"
+elif [ "${ASSETS:-0}" -eq 0 ]; then
+ note "could not read the served page from the guest (unauthenticated: expected)"
+else
+ bad "only $VER of $ASSETS asset URLs are versioned - a CSS fix can stay hidden in the browser cache"
+fi
+echo "=============================================================="
echo "REGRESSION: rDelete works (GLOB_BRACE is glibc-only; musl lacks it)"
echo "=============================================================="
# That broke deleting ANY file/folder in the editor AND removing a market plugin (the UI
diff --git a/scripts/fix-panel-layout.sh b/scripts/fix-panel-layout.sh
index bc4e753..e05afa9 100644
--- a/scripts/fix-panel-layout.sh
+++ b/scripts/fix-panel-layout.sh
@@ -73,4 +73,39 @@ EOF
|| echo " !! nginx -t failed - restore $NGX.orig"
fi
+echo "=== 3. cache-busting versioned asset URLs ==="
+# Atheos serves theme/main.min.css and the generated bundles from STABLE paths with no version:
+#
+# A browser then keeps its cached copy across a change, so a CSS/JS fix appears not to work.
+# Appending each file's mtime means a changed file gets a NEW url (fetched immediately) and an
+# unchanged one keeps its url (stays cached). Better than headers alone: it also defeats a
+# browser cache that was already poisoned before any header was set.
+SM=$ATH/classes/sourcemanager.php
+IX=$ATH/index.php
+if grep -q 'filemtime($path)' "$SM" 2>/dev/null; then
+ echo " getTag already versioned"
+else
+ [ -f "$SM.orig" ] || cp -a "$SM" "$SM.orig"
+ php83 -r '
+$f=$argv[1]; $s=file_get_contents($f);
+$old = " function getTag(\$type, \$path) {\n return \$type === \"css\" ? \"\\t\\n\": \"\\t\\n\";\n }";
+if (strpos($s,$old) === false) { fwrite(STDERR, " !! getTag signature changed - inspect $f\n"); exit(1); }
+$new = " function getTag(\$type, \$path) {\n // Version the URL by mtime so a changed asset is fetched immediately instead of being\n // served from the browser cache (docs/known-issues.md ยง5).\n if (file_exists(\$path)) {\n \$path .= \"?v=\" . filemtime(\$path);\n }\n return \$type === \"css\" ? \"\\t\\n\": \"\\t\\n\";\n }";
+file_put_contents($f, str_replace($old,$new,$s)); echo " versioned getTag\n";' "$SM"
+ php83 -l "$SM" >/dev/null 2>&1 || echo " !! SYNTAX ERROR in $SM - restore $SM.orig"
+fi
+
+if grep -q 'theme/main.min.css?v=' "$IX" 2>/dev/null; then
+ echo " index.php already versioned"
+else
+ [ -f "$IX.orig" ] || cp -a "$IX" "$IX.orig"
+ php83 -r '
+$f=$argv[1]; $s=file_get_contents($f);
+$old = " echo(\"\\t\\n\");";
+if (strpos($s,$old) === false) { fwrite(STDERR, " !! theme echo line changed - inspect $f\n"); exit(1); }
+$new = " // Version the theme URL by mtime; otherwise a browser keeps its cached copy across a\n // theme change and the fix appears not to work (docs/known-issues.md ยง5).\n \$themeV = file_exists(\"theme/main.min.css\") ? filemtime(\"theme/main.min.css\") : time();\n echo(\"\\t\\n\");";
+file_put_contents($f, str_replace($old,$new,$s)); echo " versioned index.php theme link\n";' "$IX"
+ php83 -l "$IX" >/dev/null 2>&1 || echo " !! SYNTAX ERROR in $IX - restore $IX.orig"
+fi
+
echo "=== done ==="