After you install the WhoKnows browser extension in Firefox, WhoKnows unfortunately can not automatically add the button to your browser toolbar. Here's how to do it.
1. Click the Firefox menu button.
2. Click the Customize link near the bottom of the panel.
3. You'll see the WhoKnows button in the left panel. Click and drag it up to the browser toolbar (next to the Firefox menu is fine).
4. Now, you can use the WhoKnows button to improve your profile or search for colleagues anywhere!