If you click the Remove X button on a tile on the about:newtab page then Firefox stores a hashed value of the URL in the browser.newtabpage.blocked. This is a one way encoding, so you can't check what URL this is about. You can reset this pref to unblock all web page that you have blocked.

You can change the order of the boxes on the about:newtab page and drag an item to a different tile to pin it to that position or you can remove a website by clicking the close X to block that URL. You can drag a bookmark or history item from the sidebar and drop it in a tile on the about:newtab page to pin this item and have your own favorites sites present.

Changes made manually on the about:newtab page are stored in prefs that you can find on the about:config page.

• browser.newtabpage.pinned stores websites that you have pinned to a tile.
• browser.newtabpage.blocked stores websites that you have removed by clicking the X button in a tile.

So I can still access thoughs sites, just not via tiles?

Firefox won't add a website that you blocked to a tile on the about:newtab page. Otherwise there no difference with accessing a blocked website.

If you remember what website you blocked then you can drag an history item from the history sidebar or the control center 'i' button if you have the page opened in a tab to a tile or just reset the pref via the right-click context menu to the default value.

• http://kb.mozillazine.org/about:config

That didnt really answer the question, im not consered with unblocking them from my tiles im consered with wether or not the sites are still accessable via url bar.

Rocherd said

That didnt really answer the question, im not consered with unblocking them from my tiles im consered with wether or not the sites are still accessable via url bar.

Yes. The only thing that preference is used for is to hide tiles you "X'd" off of the New Tab page.