Unlike the similar feature from Google Chrome, you can disable the page and you can remove the thumbnails you don't like.
The goal of "new tab" page is to present a list of pages you are likely to visit, but I'm not sure that it's actually useful. Opera's speed dial lets you pick the pages and this could be a better approach.
"The new tab page is the default starting point for all tabs - it is designed to get the user where they want to go, and is not meant to be an information resource like the user's home page; that is, the new tab page is not intended to be a destination, but rather a jumping-off point to other destinations - we strongly want to avoid cognitive load and distractions for the user, especially those creating new tabs for other purposes," explains Google.
If you like the feature from Chrome, but your main browser is Firefox, "new tab" page is now included in Google Toolbar. You can also try an extension that brings Opera's speed dial to Firefox.
{ Thanks, Hebbet. }
