I do not even know

migrations/541-delete-thunderbird-theme-categories.py

@@ -2,6 +2,7 @@
 
 import amo
 from addons.models import AddonCategory, Category
+from applications.models import Application
 
 
 def run():
@@ -19,7 +20,8 @@ def run():
                 fx_cat.slug, tb_cat.slug)
             AddonCategory.objects.filter(category=tb_cat).delete()
             # Get rid of `application_id` for Thunderbird category.
-            tb_cat.update(application=amo.FIREFOX.id)
+            tb_cat.update(
+                application=Application.objects.get(id=amo.FIREFOX.id))
 
     # TODO: Eventually get rid of `application_id` for all Firefox categories.
     #fx_cats.update(application=None)