don't persist form state in firefox

Fixes shelves not being disabled in dropdowns.
See https://stackoverflow.com/questions/5985839/bug-with-firefox-disabled-attribute-of-input-not-resetting-when-refreshing

bookwyrm/templates/snippets/toggle/toggle_button.html

@@ -1,6 +1,6 @@
 {% load utilities %}
 {% if fallback_url %}
-<form name="fallback_form_{{ 0|uuid }}" method="GET" action="{{ fallback_url }}">
+<form name="fallback_form_{{ 0|uuid }}" method="GET" action="{{ fallback_url }}" autocomplete="off">
 {% endif %}
 <button
     {% if not fallback_url %}