diff --git a/docs/Restrictions.md b/docs/Restrictions.md
index 38ae38b..4cb77e6 100644
--- a/docs/Restrictions.md
+++ b/docs/Restrictions.md
@@ -4,6 +4,7 @@
 
 - [Compatibility](#compatibility)
   * [Cross Platform](#cross-platform)
+  * [Firefox Version](#firefox-version)
   * [Side Effect](#side-effect)
 - [Internals](#internals)
   * [CSS Loading Order](#css-loading-order)
@@ -23,6 +24,24 @@ For example, The appearance of the context menu varies from platform to platform
 
 Consider compatibility as much as possible, but use [dedicated media queries](https://github.com/mozilla/gecko-dev/blob/d6188c9ce02efeea309e7177fc14c9eb2f09db37/servo/components/style/gecko/media_features.rs#L906-L930) in special cases.
 
+[Bookmark menu](https://github.com/black7375/Firefox-UI-Fix/issues/136) is also similar example([code](https://github.com/black7375/Firefox-UI-Fix/blob/36e9c94844fee2417662251cbd50c2b874d5b576/userChrome.css#L4745-L4840)).
+
+### Firefox Version
+There may be changes that change by version of Firefox.
+
+It's [more frequent than your thought](https://github.com/black7375/Firefox-UI-Fix/issues?q=is%3Aissue+label%3Aupstream+), and we need to respond to compatibility between [Nightly](https://www.mozilla.org/en-US/firefox/nightly/notes/) and [ESR](https://www.mozilla.org/en-US/firefox/organizations/notes/) versions.
+
+This project is using SCSS to make a reusable compatible mixins.
+```scss
+@include OS($linux) {
+  // Your CSS`
+}
+
+@include Dark {
+  // Your CSS`
+}
+```
+
 ### 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).
 
@@ -45,6 +64,10 @@ To modify, it is often a roundabout approach or impossible to inherit
 ### XUL
 Sometimes firefox can use [XUL](https://en.wikipedia.org/wiki/XUL) that have been written and binded with C++ for performance like a treeview of bookmarks.
 
-The proper document does not exist, so we have to read the source code and work.
+There ar few appropriate documents, so we have to read the source code and work. (Ex. [1](https://github.com/mozilla/gecko-dev/blob/master/layout/style/nsCSSAnonBoxList.h), [2](https://github.com/mozilla/gecko-dev/blob/master/layout/xul/tree/nsITreeView.idl))
 
 Available CSS features are also restricted.
+
+Example of legacy documents that will help.
+- [UDN: ::-moz-tree-cell](https://udn.realityripple.com/docs/Mozilla/Gecko/Chrome/CSS/::-moz-tree-cell)
+- [UDN: ::-moz-tree-cell-text](https://udn.realityripple.com/docs/Mozilla/Gecko/Chrome/CSS/::-moz-tree-cell-text)