diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index a766cd2..7bdb5cf 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -418,6 +418,10 @@
       }
     }
   },
+  "Extension_list": {
+    "message": "Intercept download of files with those extensions (space/colon separated)",
+    "description": "Header for settings section."
+  },
   "Debugging_Output": {
     "message": "Debugging Output",
     "description": "Header for settings section."
diff --git a/src/background/backgroundState.ts b/src/background/backgroundState.ts
index 2e6eecb..a586c77 100644
--- a/src/background/backgroundState.ts
+++ b/src/background/backgroundState.ts
@@ -11,6 +11,7 @@ export interface BackgroundState {
   notificationInterval: number | undefined;
   showNonErrorNotifications: boolean;
   isInitializingExtension: boolean;
+  interceptExtensions: string;
 }
 
 const state: BackgroundState = {
@@ -21,6 +22,7 @@ const state: BackgroundState = {
   notificationInterval: undefined,
   showNonErrorNotifications: true,
   isInitializingExtension: true,
+  interceptExtensions: '',
 };
 
 export function getMutableStateSingleton() {
diff --git a/src/background/downloadInterceptor.ts b/src/background/downloadInterceptor.ts
new file mode 100644
index 0000000..c3f7413
--- /dev/null
+++ b/src/background/downloadInterceptor.ts
@@ -0,0 +1,30 @@
+import { getMutableStateSingleton } from "./backgroundState";
+import { addDownloadTasksAndPoll } from "./actions";
+
+export function initializeDownloadInterceptor() {
+  downloads.onCreated.addListener((itm)=>{
+
+    const state = getMutableStateSingleton();
+    var ext, ext_list;
+
+    ext_list = state.interceptExtensions.split(' ');
+
+    // has no extension
+    if (itm.filename.index('.') < 0) return;
+
+    ext = itm.filename.split('.').pop().toLowerCase();
+
+    // extension not in the list
+    if (ext_list.indexOf(ext) < 0) return;
+
+    // stop download and add NAS task
+    downloads.cancel(itm.id);
+    addDownloadTasksAndPoll(
+      state.api,
+      state.pollRequestManager,
+      state.showNonErrorNotifications,
+      [itm.url],
+    );
+
+  });
+}
diff --git a/src/background/index.ts b/src/background/index.ts
index 7638916..bdbaea6 100644
--- a/src/background/index.ts
+++ b/src/background/index.ts
@@ -4,9 +4,11 @@ import { saveLastSevereError } from "../common/errorHandlers";
 import { onStoredStateChange as onStoredStateChangeListener } from "./onStateChange";
 import { initializeContextMenus } from "./contextMenus";
 import { initializeMessageHandler } from "./messages";
+import { initializeDownloadInterceptor } from "./downloadInterceptor";
 
 initializeContextMenus();
 initializeMessageHandler();
+initializeDownloadInterceptor();
 
 maybeMigrateState()
   .then(() => {
diff --git a/src/background/onStateChange.ts b/src/background/onStateChange.ts
index 6dd1dd9..b048f61 100644
--- a/src/background/onStateChange.ts
+++ b/src/background/onStateChange.ts
@@ -133,5 +133,7 @@ export function onStoredStateChange(storedState: State) {
     backgroundState.finishedTaskIds = new Set(updatedFinishedTaskIds);
   }
 
+  backgroundState.interceptExtensions = storedState.settings.interceptExtensions;
+
   backgroundState.isInitializingExtension = false;
 }
diff --git a/src/common/state/listen.ts b/src/common/state/listen.ts
index 059a92f..0266400 100644
--- a/src/common/state/listen.ts
+++ b/src/common/state/listen.ts
@@ -9,6 +9,7 @@ export const SETTING_NAMES = typesafeUnionMembers<keyof Settings>({
   shouldHandleDownloadLinks: true,
   badgeDisplayType: true,
   showInactiveTasks: true,
+  interceptExtensions: true,
 });
 
 const ALL_STORED_STATE_NAMES = typesafeUnionMembers<keyof State>({
diff --git a/src/settings/SettingsForm.tsx b/src/settings/SettingsForm.tsx
index af0f137..2b5efc4 100644
--- a/src/settings/SettingsForm.tsx
+++ b/src/settings/SettingsForm.tsx
@@ -160,6 +160,23 @@ export class SettingsForm extends React.PureComponent<Props, State> {
               DOWNLOAD_ONLY_PROTOCOLS.join(", "),
             ])}
           />
+
+          <span className="label">{browser.i18n.getMessage("Extension_list")}</span>
+          <div className="input">
+            <input
+              type="text"
+              value={this.props.extensionState.settings.interceptExtensions}
+              onChange={(e) => {
+                var interceptExtensions = e.currentTarget.value
+                  .replace(/[\;\,\.]/g,' ')// unify various separators into spaces
+                  .toLowerCase()
+                  .split(' ')
+                  .filter((s)=>{ return s; })
+                  .join(' ');
+                this.saveExtList(interceptExtensions);
+              }}
+            />
+          </div>
         </SettingsList>
 
         {this.maybeRenderDebuggingOutputAndSeparator()}
@@ -265,6 +282,12 @@ export class SettingsForm extends React.PureComponent<Props, State> {
     });
   }
 
+  private saveExtList(interceptExtensions: string) {
+    this.saveSettings({
+      interceptExtensions,
+    });
+  }
+
   private saveSettings = async (settings: Partial<Settings>) => {
     const success = await this.props.saveSettings({
       ...typesafePick(this.props.extensionState.settings, ...SETTING_NAMES),