I forgot to address the review comment when relanding this.

browser/components/help/locale/en-US/prefs.xhtml

@@ -415,7 +415,7 @@ Contributors:
     allowing you to select text with the keyboard. Some accessibility aids, such
     as screen readers and screen magnifiers, use the system caret to determine
     which area of the screen to read or magnify. You can toggle this mode by
-    pressing F7.</p>
+    pressing <kbd>F7</kbd>.</p>
 
   <p><em>Begin finding as you begin typing</em><br/>When this &pref.singular; is
     enabled, &brandShortName; will find within the current web page what you