Have you tried emptying the cache and deleting cookies?

Hi   ! Assuming that you're talking about the thumbnails on the New Tab Page and somehow for you clicking on the 'x' in the top right corner of a thumbnail doesn't work, you could create a new Boolean preference in 'about:config' :

Type in the address bar   about:config   (press Enter) (promise to be careful, if asked) Right-click on the page and select 'Boolean' enter the preference :

browser.pagethumbnails.capturing_disabled

and set it's value to   true

Click   'OK'

See : http://kb.mozillazine.org/About:config#Adding_modifying_and_resetting_preferences

Note that the thumbnails are stored in the thumbnails folder that is in the same location as the disk cache. See the about:profiles page for the location and a button to go to this folder. Go up one level to see the thumbnails folder.

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.