Message: "A script in the Norton extension is causing Firefox to slow down"

Start Mozilla Firefox.

On the top-right corner, click the Open menu button.

Click Help, and then click About Firefox.

Firefox checks for updates and downloads them automatically.

Click Restart to update Firefox.

Start Mozilla Firefox.

On the top-right corner, click the Open menu button.

Click Add-ons.

In the Add-ons window, click Extensions in the left pane.

On the top of the page, click on the Gear icon, and then click Check for Updates.