It's normal for Firefox to create thumbnails of pages in your history, but usually the new tab page fills up with heavily visited sites and rarely shows new sites so it's odd to see them show up there right away (unless you clear your history frequently).

Do you want to change what shows on a new tab? There's a hidden setting for that:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste newtab and pause while the list is filtered

(3) Double-click the browser.newtab.url preference and enter your preferred page:

• Page thumbnails (default) => about:newtab
• Blank tab => about:blank
• Built-in Firefox home page => about:home
• Any other page => full URL to the page

Press Ctrl+t to open a new tab and verify that it worked. Fixed?

You can create this Boolean pref on the about:config page to prevent Firefox from generating thumbnails for the about:newtab page.

• name: browser.pagethumbnails.capturing_disabled with value: true
• https://developer.mozilla.org/Mozilla/Preferences/Preference_reference/browser.pagethumbnails.capturing_disabled

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

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

Delete the thumbnails folder in the Firefox profile folder to remove already stored web page thumbnails. You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

Thanks, it fixed the problem. I'm not really sure why It did that, I think it was a bug in the update or something.