From eb726d98f5b0e7eec9c195f0e3a1cb52b30f2eea Mon Sep 17 00:00:00 2001
From: alstjr7375 <alstjr7375@daum.net>
Date: Tue, 12 Apr 2022 17:01:59 +0900
Subject: [PATCH] Doc: Restrictions - XUL sideeffect by @MrOtherGuy

https://www.reddit.com/r/FirefoxCSS/comments/u1mdld/comment/i4eg29n/?utm_source=share&utm_medium=web2x&context=3
---
 docs/Restrictions.md | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/docs/Restrictions.md b/docs/Restrictions.md
index 6d7954c..e70e6f3 100644
--- a/docs/Restrictions.md
+++ b/docs/Restrictions.md
@@ -51,6 +51,14 @@ This project is using SCSS to make a [reusable compatible mixins](../src/utils).
 ### Side Effect
 Only CSS modifications can cause bugs that are hard to think of in the general web, such as the [context menu not appearing](https://github.com/black7375/Firefox-UI-Fix/issues/114).
 
+Especially be careful when customizing XUL elements.  
+The following code will cause extension panels fail to open and trying to open them might even crash Firefox. (@MrOtherGuy reports)
+```css
+#nav-bar {
+  display: flex;
+}
+```
+
 ## Internals
 ### CSS Loading Order
 User CSS(`userChrome.css`, `userContent.css`) is usually loaded first.