Add comment about how remembering passwords doesn't work.

packages/accounts-ui-unstyled/login_buttons_dropdown.html

@@ -156,6 +156,26 @@
   </div>
 </template>
 
+
+<!--
+This strategy for login forms means that browsers' "Remember password"
+functionality does not work. Different browsers have different
+requirements for remembering passwords:
+
+- Firefox: Must be an actual form (with a submit button), but you can
+cancel the submit with onsubmit='return false'.
+
+- Safari: Must be an actual form, and the form must actually be
+submitted somewhere (though it can target a hidden iframe and go to a
+bogus URL)
+
+- Chrome: Must be an actual form, and the the form elements must be
+present in the initial HTML, not added to the page with javascript. This
+basically rules out using normal meteor templates.
+
+https://gist.github.com/968927
+-->
+
 <template name="_loginButtonsFormField">
   {{#if visible}}
     <div id="login-{{fieldName}}-label-and-input">