Firefox: Tools > Addons > Plugins Tab > disable all
Don't use Flashblock or Javablock or similar extensions, they hide the applet, they don't stop execution.
You should always use a browser with all plugins disabled as your default browser. Run a second browser for trusted sites where you enter the URL in yourself.
In Chrome: go to chrome://plugins and disable all
Safari: Preferences, Security uncheck 'Enable Plugins'
Firefox: Tools > Addons > Plugins Tab > disable all
Don't use Flashblock or Javablock or similar extensions, they hide the applet, they don't stop execution.
You should always use a browser with all plugins disabled as your default browser. Run a second browser for trusted sites where you enter the URL in yourself.