diff --git a/dev/Knoin/Knoin.js b/dev/Knoin/Knoin.js
index 8636c7166..b69bfeab1 100644
--- a/dev/Knoin/Knoin.js
+++ b/dev/Knoin/Knoin.js
@@ -51,6 +51,7 @@ const
 
 					// Firefox < 98 / Safari < 15.4 HTMLDialogElement not defined
 					if (!vmDom.showModal) {
+						vmDom.className = 'polyfill';
 						vmDom.showModal = () => {
 							vmDom.backdrop ||
 								vmDom.before(vmDom.backdrop = Element.fromHTML('<div class="dialog-backdrop"></div>'));
diff --git a/integrations/nextcloud/snappymail/css/embed.css b/integrations/nextcloud/snappymail/css/embed.css
index 0df67cffa..130035ffb 100644
--- a/integrations/nextcloud/snappymail/css/embed.css
+++ b/integrations/nextcloud/snappymail/css/embed.css
@@ -105,6 +105,15 @@ body > header ul {
 	cursor: pointer;
 }
 
+/**
+ * Firefox < 98
+ * https://github.com/the-djmaze/snappymail/issues/673
+ */
+#rl-app dialog.polyfill {
+	margin-top: 50px;
+	max-height: calc(100vh - 60px);
+}
+
 /**
  * hampoelz
  * https://github.com/the-djmaze/snappymail/issues/96#issuecomment-1279783076