diff --git a/modules/programs/firefox.nix b/modules/programs/firefox.nix
index 2a2667c35..853c3385b 100644
--- a/modules/programs/firefox.nix
+++ b/modules/programs/firefox.nix
@@ -1,15 +1,11 @@
 { lib, ... }:
-
 with lib;
-
 let
-
   modulePath = [ "programs" "firefox" ];
 
   moduleName = concatStringsSep "." modulePath;
 
   mkFirefoxModule = import ./firefox/mkFirefoxModule.nix;
-
 in {
   meta.maintainers = [ maintainers.rycee hm.maintainers.bricked ];
 
@@ -32,14 +28,13 @@ in {
     })
 
     (mkRemovedOptionModule (modulePath ++ [ "extensions" ]) ''
-
       Extensions are now managed per-profile. That is, change from
 
         ${moduleName}.extensions = [ foo bar ];
 
       to
 
-        ${moduleName}.profiles.myprofile.extensions = [ foo bar ];'')
+        ${moduleName}.profiles.myprofile.extensions.packages = [ foo bar ];'')
     (mkRemovedOptionModule (modulePath ++ [ "enableAdobeFlash" ])
       "Support for this option has been removed.")
     (mkRemovedOptionModule (modulePath ++ [ "enableGoogleTalk" ])
diff --git a/modules/programs/firefox/mkFirefoxModule.nix b/modules/programs/firefox/mkFirefoxModule.nix
index 76954dd9c..115af89d9 100644
--- a/modules/programs/firefox/mkFirefoxModule.nix
+++ b/modules/programs/firefox/mkFirefoxModule.nix
@@ -1,13 +1,9 @@
 { modulePath, name, description ? null, wrappedPackageName ? null
 , unwrappedPackageName ? null, platforms, visible ? false
-, enableBookmarks ? true }:
-
+, enableBookmarks ? true, }:
 { config, lib, pkgs, ... }:
-
 with lib;
-
 let
-
   inherit (pkgs.stdenv.hostPlatform) isDarwin;
 
   appName = name;
@@ -77,11 +73,13 @@ let
     else
       builtins.toJSON pref);
 
-  mkUserJs = prePrefs: prefs: extraPrefs: bookmarks:
+  mkUserJs = prePrefs: prefs: extraPrefs: bookmarks: extensions:
     let
       prefs' = lib.optionalAttrs ([ ] != bookmarks) {
         "browser.bookmarks.file" = toString (browserBookmarksFile bookmarks);
         "browser.places.importBookmarksHTML" = true;
+      } // lib.optionalAttrs (extensions != { }) {
+        "extensions.webextensions.ExtensionStorageIDB.enabled" = false;
       } // prefs;
     in ''
       // Generated by Home Manager.
@@ -218,7 +216,6 @@ let
 
       # The configuration expected by the Firefox wrapper builder.
       bcfg = setAttrByPath [ browserName ] fcfg;
-
     in if package == null then
       null
     else if isDarwin then
@@ -230,7 +227,6 @@ let
       })
     else
       (pkgs.wrapFirefox.override { config = bcfg; }) package { };
-
 in {
   options = setAttrByPath modulePath {
     enable = mkOption {
@@ -242,7 +238,7 @@ in {
           optionalString (description != null) " ${description}"
         }
         ${optionalString (!visible)
-        "See `programs.firefox` for more configuration options."}
+        "See `${moduleName}` for more configuration options."}
       '';
     };
 
@@ -667,37 +663,114 @@ in {
               for more information.
             '';
           };
-
           extensions = mkOption {
-            type = types.listOf types.package;
-            default = [ ];
-            example = literalExpression ''
-              with pkgs.nur.repos.rycee.firefox-addons; [
-                privacy-badger
-              ]
-            '';
+            type = types.coercedTo (types.listOf types.package) (packages: {
+              packages = mkIf (builtins.length packages > 0) (warn ''
+                In order to support declarative extension configuration,
+                extension installation has been moved from
+                ${moduleName}.profiles.<profile>.extensions
+                to
+                ${moduleName}.profiles.<profile>.extensions.packages
+              '' packages);
+            }) (types.submodule {
+              options = {
+                packages = mkOption {
+                  type = types.listOf types.package;
+                  default = [ ];
+                  example = literalExpression ''
+                    with pkgs.nur.repos.rycee.firefox-addons; [
+                      privacy-badger
+                    ]
+                  '';
+                  description = ''
+                    List of ${name} add-on packages to install for this profile.
+                    Some pre-packaged add-ons are accessible from the Nix User Repository.
+                    Once you have NUR installed run
+
+                    ```console
+                    $ nix-env -f '<nixpkgs>' -qaP -A nur.repos.rycee.firefox-addons
+                    ```
+
+                    to list the available ${name} add-ons.
+
+                    Note that it is necessary to manually enable these extensions
+                    inside ${name} after the first installation.
+
+                    To automatically enable extensions add
+                    `"extensions.autoDisableScopes" = 0;`
+                    to
+                    [{option}`${moduleName}.profiles.<profile>.settings`](#opt-${moduleName}.profiles._name_.settings)
+                  '';
+                };
+
+                settings = mkOption {
+                  default = { };
+                  example = literalExpression ''
+                    {
+                      # Example with uBlock origin's extensionID
+                      "uBlock0@raymondhill.net".settings = {
+                        selectedFilterLists = [
+                          "ublock-filters"
+                          "ublock-badware"
+                          "ublock-privacy"
+                          "ublock-unbreak"
+                          "ublock-quick-fixes"
+                        ];
+                      };
+
+                      # Example with Stylus' UUID-form extensionID
+                      "{7a7a4a92-a2a0-41d1-9fd7-1e92480d612d}".settings = {
+                        dbInChromeStorage = true; # required for Stylus
+                      }
+                    }
+                  '';
+                  description = ''
+                    Attribute set of options for each extension.
+                    The keys of the attribute set consist of the ID of the extension
+                    or its UUID wrapped in curly braces.
+                  '';
+                  type = types.attrsOf (types.submodule {
+                    options = {
+                      settings = mkOption {
+                        type = types.attrsOf jsonFormat.type;
+                        description =
+                          "Json formatted options for the specified extensionID";
+                      };
+                      force = mkOption {
+                        type = types.bool;
+                        default = false;
+                        example = true;
+                        description = ''
+                          Forcibly override any existing configuration for
+                          this extension.
+                        '';
+                      };
+                    };
+                  });
+                };
+              };
+            });
+            default = { };
             description = ''
-              List of ${appName} add-on packages to install for this profile.
-              Some pre-packaged add-ons are accessible from the
-              [Nix User Repository](https://github.com/nix-community/NUR).
-              Once you have NUR installed run
-
-              ```console
-              $ nix-env -f '<nixpkgs>' -qaP -A nur.repos.rycee.firefox-addons
-              ```
-
-              to list the available ${appName} add-ons.
-
-              Note that it is necessary to manually enable these extensions
-              inside ${appName} after the first installation.
-
-              To automatically enable extensions add
-              `"extensions.autoDisableScopes" = 0;`
-              to
-              [{option}`${moduleName}.profiles.<profile>.settings`](#opt-${moduleName}.profiles._name_.settings)
+              Submodule for installing and configuring extensions.
+            '';
+            example = literalExpression ''
+              {
+                packages = with pkgs.nur.repos.rycee.firefox-addons; [
+                  ublock-origin
+                ];
+                settings."uBlock0@raymondhill.net".settings = {
+                  selectedFilterLists = [
+                    "ublock-filters"
+                    "ublock-badware"
+                    "ublock-privacy"
+                    "ublock-unbreak"
+                    "ublock-quick-fixes"
+                  ];
+                };
+              }
             '';
           };
-
         };
       }));
       default = { };
@@ -748,7 +821,7 @@ in {
       {
         assertion = cfg.languagePacks == [ ] || cfg.package != null;
         message = ''
-          'programs.firefox.languagePacks' requires 'programs.firefox.package'
+          '${moduleName}.languagePacks' requires '${moduleName}.package'
           to be set to a non-null value.
         '';
       }
@@ -776,47 +849,59 @@ in {
           "${nativeMessagingHostsJoined}/lib/mozilla/native-messaging-hosts";
         recursive = true;
       };
-    } ++ flip mapAttrsToList cfg.profiles (_: profile: {
-      "${profilesPath}/${profile.path}/.keep".text = "";
+    } ++ flip mapAttrsToList cfg.profiles (_: profile:
+      # Merge the regular profile settings with extension settings
+      mkMerge ([{
+        "${profilesPath}/${profile.path}/.keep".text = "";
 
-      "${profilesPath}/${profile.path}/chrome/userChrome.css" =
-        mkIf (profile.userChrome != "") { text = profile.userChrome; };
+        "${profilesPath}/${profile.path}/chrome/userChrome.css" =
+          mkIf (profile.userChrome != "") { text = profile.userChrome; };
 
-      "${profilesPath}/${profile.path}/chrome/userContent.css" =
-        mkIf (profile.userContent != "") { text = profile.userContent; };
+        "${profilesPath}/${profile.path}/chrome/userContent.css" =
+          mkIf (profile.userContent != "") { text = profile.userContent; };
 
-      "${profilesPath}/${profile.path}/user.js" = mkIf (profile.preConfig != ""
-        || profile.settings != { } || profile.extraConfig != ""
-        || profile.bookmarks != [ ]) {
-          text = mkUserJs profile.preConfig profile.settings profile.extraConfig
-            profile.bookmarks;
-        };
+        "${profilesPath}/${profile.path}/user.js" = mkIf (profile.preConfig
+          != "" || profile.settings != { } || profile.extraConfig != ""
+          || profile.bookmarks != [ ]) {
+            text =
+              mkUserJs profile.preConfig profile.settings profile.extraConfig
+              profile.bookmarks profile.extensions.settings;
+          };
 
-      "${profilesPath}/${profile.path}/containers.json" =
-        mkIf (profile.containers != { }) {
-          text = mkContainersJson profile.containers;
-          force = profile.containersForce;
-        };
+        "${profilesPath}/${profile.path}/containers.json" =
+          mkIf (profile.containers != { }) {
+            text = mkContainersJson profile.containers;
+            force = profile.containersForce;
+          };
 
-      "${profilesPath}/${profile.path}/search.json.mozlz4" =
-        mkIf (profile.search.enable) {
-          enable = profile.search.enable;
-          force = profile.search.force;
-          source = profile.search.file;
-        };
+        "${profilesPath}/${profile.path}/search.json.mozlz4" =
+          mkIf (profile.search.enable) {
+            enable = profile.search.enable;
+            force = profile.search.force;
+            source = profile.search.file;
+          };
 
-      "${profilesPath}/${profile.path}/extensions" =
-        mkIf (profile.extensions != [ ]) {
-          source = let
-            extensionsEnvPkg = pkgs.buildEnv {
-              name = "hm-firefox-extensions";
-              paths = profile.extensions;
-            };
-          in "${extensionsEnvPkg}/share/mozilla/${extensionPath}";
-          recursive = true;
-          force = true;
-        };
-    }));
+        "${profilesPath}/${profile.path}/extensions" =
+          mkIf (profile.extensions.packages != [ ]) {
+            source = let
+              extensionsEnvPkg = pkgs.buildEnv {
+                name = "hm-firefox-extensions";
+                paths = profile.extensions.packages;
+              };
+            in "${extensionsEnvPkg}/share/mozilla/${extensionPath}";
+            recursive = true;
+            force = true;
+          };
+      }] ++
+        # Add extension settings as separate attributes
+        optional (profile.extensions.settings != { }) (mkMerge (mapAttrsToList
+          (name: settingConfig: {
+            "${profilesPath}/${profile.path}/browser-extension-data/${name}/storage.js" =
+              {
+                force = settingConfig.force;
+                text = generators.toJSON { } settingConfig.settings;
+              };
+          }) profile.extensions.settings)))));
   } // setAttrByPath modulePath {
     finalPackage = wrapPackage cfg.package;
 
diff --git a/tests/modules/programs/firefox/profiles/extensions/default.nix b/tests/modules/programs/firefox/profiles/extensions/default.nix
new file mode 100644
index 000000000..577518390
--- /dev/null
+++ b/tests/modules/programs/firefox/profiles/extensions/default.nix
@@ -0,0 +1,31 @@
+modulePath:
+{ config, lib, pkgs, ... }:
+with lib;
+let
+  cfg = getAttrFromPath modulePath config;
+
+  firefoxMockOverlay = import ../../setup-firefox-mock-overlay.nix modulePath;
+in {
+  imports = [ firefoxMockOverlay ];
+
+  config = mkIf config.test.enableBig (setAttrByPath modulePath {
+    enable = true;
+    profiles.extensions = {
+      extensions.settings."uBlock0@raymondhill.net".settings = {
+        selectedFilterLists = [
+          "ublock-filters"
+          "ublock-badware"
+          "ublock-privacy"
+          "ublock-unbreak"
+          "ublock-quick-fixes"
+        ];
+      };
+    };
+  } // {
+    nmt.script = ''
+      assertFileContent \
+        home-files/${cfg.configPath}/extensions/uBlock0@raymondhill.net/storage.js \
+        ${./expected-storage.js}
+    '';
+  });
+}
diff --git a/tests/modules/programs/firefox/profiles/extensions/expected-storage.js b/tests/modules/programs/firefox/profiles/extensions/expected-storage.js
new file mode 100644
index 000000000..66c2a8d0f
--- /dev/null
+++ b/tests/modules/programs/firefox/profiles/extensions/expected-storage.js
@@ -0,0 +1 @@
+{"selectedFilterLists":["ublock-filters","ublock-badware","ublock-privacy","ublock-unbreak","ublock-quick-fixes"]}