It takes all of your tabs (choose between all/all-except-current/current/all-to-right/all-to-left) and turns them into links in a special OneTab tab where you can further manage your tabs by dividing them into groups, removing duplicates and securing them so that they can't be removed unless un...
Everything that wasn't added by Valve to the web-based page is added through this extension. Price changes and regional difference, colors for wishlisted/owned/uninterested games, transaction history, and many many other really useful and cool features.
AdBlock+ has an automatic whitelist when installed that allows certain advertisers through the blocking mechanism. The fact that these advertisers pay for this privilege makes this particular scenario rife with conflict of interest.