feat: update Zen browser version to 1.12.3b; change default browser to Firefox in dconf and default apps configuration

config/home-manager/flake.lock

@@ -7,11 +7,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1745557122,
-        "narHash": "sha256-eqSo9ugzsqhFgaDFYUZj943nurlX4L6f+AW0skJ4W+M=",
+        "lastModified": 1747020534,
+        "narHash": "sha256-D/6rkiC6w2p+4SwRiVKrWIeYzun8FBg7NlMKMwQMxO0=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "dd26f75fb4ec1c731d4b1396eaf4439ce40a91c1",
+        "rev": "b4bbdc6fde16fc2051fcde232f6e288cd22007ca",
         "type": "github"
       },
       "original": {
@@ -23,11 +23,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1745742390,
-        "narHash": "sha256-1rqa/XPSJqJg21BKWjzJZC7yU0l/YTVtjRi0RJmipus=",
+        "lastModified": 1746957726,
+        "narHash": "sha256-k9ut1LSfHCr0AW82ttEQzXVCqmyWVA5+SHJkS5ID/Jo=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "26245db0cb552047418cfcef9a25da91b222d6c7",
+        "rev": "a39ed32a651fdee6842ec930761e31d1f242cb94",
         "type": "github"
       },
       "original": {
@@ -39,11 +39,11 @@
     },
     "nixpkgs-unstable": {
       "locked": {
-        "lastModified": 1745794561,
-        "narHash": "sha256-T36rUZHUART00h3dW4sV5tv4MrXKT7aWjNfHiZz7OHg=",
+        "lastModified": 1746904237,
+        "narHash": "sha256-3e+AVBczosP5dCLQmMoMEogM57gmZ2qrVSrmq9aResQ=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "5461b7fa65f3ca74cef60be837fd559a8918eaa0",
+        "rev": "d89fc19e405cb2d55ce7cc114356846a0ee5e956",
         "type": "github"
       },
       "original": {