diff --git a/spec/selenium_spec_marionette.rb b/spec/selenium_spec_marionette.rb
index 0db3e068..0038594c 100644
--- a/spec/selenium_spec_marionette.rb
+++ b/spec/selenium_spec_marionette.rb
@@ -61,6 +61,8 @@ Capybara::SpecHelper.run_specs TestSessions::SeleniumMarionette, 'selenium', cap
             'if files are already set'
   when 'Capybara::Session selenium #attach_file with multipart form should fire change once when uploading multiple files from empty'
     pending "FF < 62 doesn't support setting all files at once" if marionette_lt?(62, @session)
+  when 'Capybara::Session selenium #accept_confirm should work with nested modals'
+    skip 'Broken in FF 63 - https://bugzilla.mozilla.org/show_bug.cgi?id=1487358' if marionette_gte?(63, @session)
   end
 end