Fix menus and attempt to make stuff native

Author: K4sum1

browser/components/aboutwelcome/content/aboutwelcome.css

@@ -34,7 +34,6 @@
   outline: none;
   color: var(--fc-color);
   accent-color: var(--fc-accent-color);
-  -moz-theme: non-native;
   --arrow-width: 33.9411px;
   --arrow-square-size: calc(var(--arrow-width) / sqrt(2));
   --extra-width-from-rotation: calc(var(--arrow-width) - var(--arrow-square-size));

toolkit/themes/shared/in-content/common-shared.css

@@ -104,7 +104,6 @@
   --card-outline-color: var(--grey-30);
   --card-shadow-hover: var(--card-shadow), 0 0 0 5px var(--card-outline-color);
 
-  -moz-theme: non-native;
   accent-color: var(--in-content-accent-color);
   color-scheme: light dark;
 }
@@ -549,7 +548,7 @@ xul|menulist > xul|menupopup {
 
   --panel-border-color: var(--in-content-box-border-color);
   --panel-border-radius: 2px;
-  --panel-background: var(--in-content-box-background);
+  --panel-background: var(--in-content-table-background);
   --panel-color: var(--in-content-text-color);
   --panel-padding: 0;
 }