new file

chrome/autohide_navigation_button.css

@@ -0,0 +1,33 @@
+/* Hides navigation-buttons (back/forward/stop/reload) buttons and shows them when cursor is over the right edge of urlbar  */
+/* Disabled button are completely hidden, such as back-button when there is no page to go back to */
+
+/* To set this up you need to customize the order of items to be such that layout from LEFT to RIGHT is 
+urlbar
+flexible space
+navigation-buttons in any order
+ */
+/* The order of items before urlbar and after navigation-buttons doesn't matter */
+
+#nav-bar-customization-target > toolbarbutton.chromeclass-toolbar-additional[overflows="false"],
+#nav-bar-customization-target > #stop-reload-button > #reload-button{
+  margin-inline-start: -30px !important;
+  visibility:hidden;
+  transition: margin 66ms linear !important
+}
+
+#nav-bar-customization-target > .chromeclass-toolbar-additional[overflows="false"]:hover,
+#nav-bar-customization-target > .chromeclass-toolbar-additional[overflows="false"]:hover ~ .chromeclass-toolbar-additional[overflows="false"],
+#nav-bar-customization-target > .chromeclass-toolbar-additional[overflows="false"]:hover ~ #stop-reload-button > #reload-button,
+#nav-bar-customization-target > #urlbar-container + toolbarspring:hover ~ .chromeclass-toolbar-additional[overflows="false"],
+#nav-bar-customization-target > #stop-reload-button:hover > #reload-button,
+#nav-bar-customization-target > #urlbar-container + toolbarspring:hover ~ #stop-reload-button > #reload-button{
+  margin-inline-start: 0px !important;
+  visibility: visible
+}
+
+#nav-bar-customization-target > #downloads-button { margin-inline-start: 0px !important; visibility: visible !important; }
+
+#nav-bar-customization-target > toolbarbutton.chromeclass-toolbar-additional[overflows="false"][disabled],
+#nav-bar-customization-target > #stop-reload-button > [disabled]{ display: none }
+
+#urlbar-container + toolbarspring{ max-width: 4px !important; min-width: 4px !important; }