Since not everyone is getting this notice, you should grab the Gamebar by clicking here to go directly to the official download page. Next, click on "Download Gamebar" for a 2.4MB file with the name: FFCrowdstarToolbarInstaller_CDS_tbr_220.127.116.11.exe
Judging by the file name, you should be able to tell that this Gamebar is a newer edition than the one released in April, so maybe you'd want to keep it around to test it out.
After you've downloaded the Gamebar, double-click on it to run installation, then restart your browser. When you log back in, you should see the image below. Click on "Get My Shark!" and you'll get a baby Rare Rainbow Shark in your tank.
If you're using Firefox, simply go to the top of your window for the "Tools" menu, scroll down to "Add-ons", look for the "Crowdstar Gamebar", then click "Uninstall". Firefox will restart itself, the Gamebar will be gone, and you'll get to keep the shark!
For Internet Explorer users, go to "Tools", scroll down to "Manage Add-ons", look for the "Crowdstar Gamebar" listed under "Ask.com", double-click on the name "Crowdstar Gamebar", then click on "Remove".