[cookies] Add `--cookies-from-browser` support for Firefox Flatpak (#9619)

Authored by: un-def

yt_dlp/cookies.py

@@ -194,7 +194,11 @@ def _firefox_browser_dirs():
         yield os.path.expanduser('~/Library/Application Support/Firefox/Profiles')
 
     else:
-        yield from map(os.path.expanduser, ('~/.mozilla/firefox', '~/snap/firefox/common/.mozilla/firefox'))
+        yield from map(os.path.expanduser, (
+            '~/.mozilla/firefox',
+            '~/snap/firefox/common/.mozilla/firefox',
+            '~/.var/app/org.mozilla.firefox/.mozilla/firefox',
+        ))
 
 
 def _firefox_cookie_dbs(roots):