Are you talking about the New Tab page?
https://support.mozilla.org/en-US/kb/new-tab-page-show-hide-and-customize-top-sites

Problem solved. That sure was easy. The one icon I didn't try. Thank You

You can also set the browser.newtab.url pref to about:blank if you do not want to use the about:newtab page instead of disabling this page via the icon in the top right corner.

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

Note that Firefox still creates thumbnails of visited pages in the thumbnails folder when you disable the about:newtab page.

• http://kb.mozillazine.org/Profile_folder_-_Firefox

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

• name: browser.pagethumbnails.capturing_disabled with value: true
• name: pageThumbs.enabled with value: false

Delete the thumbnails folder in the Firefox profile folder to remove already stored web page thumbnails.