feat(minion): add firefox sidebery customizations

I use sidebery on firefox, but sidebery is not best used without hiding
some existing firefox elements such as the original tab bar

Change-Id: I4b9af3df468e0bea92517d3bf7050c42535ad9fa
Reviewed-on: https://git.clicks.codes/c/Chimera/NixFiles/+/706
Reviewed-by: Skyler Grey <minion@clicks.codes>
Tested-by: Skyler Grey <minion@clicks.codes>
diff --git a/flake.nix b/flake.nix
index a40d052..4b6fc1e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -21,6 +21,11 @@
       flake = false;
     };
 
+    firefox-sidebery-gnome = {
+      url = "github:rafaelmardojai/firefox-gnome-theme";
+      flake = false;
+    };
+
     home-manager = {
       url = "github:nix-community/home-manager";
       inputs.nixpkgs.follows = "nixpkgs";