You can remove the google search bar by clicking the grey square (it has many little squares in it) this will hide the new tab page however this will also remove the sites you have recently been on.

if you want to get rid of google completely there 'may' be 2 search boxes at the top, the big one and then the small on for your search engine (google by default i believe), you can change the search engine or remove that little search bar completely by clicking on the Firefox menu (the symbol with 3 grey lines at the top right) then click on customise and then drag the google search box away, then click exit customisation :)

You can add code to the userContent.css file to hide the search bar on the about:newtab page.

• http://kb.mozillazine.org/userContent.css

@-moz-document url(about:newtab){
#newtab-margin-top, #newtab-search-container { display:none !important; }
}

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

• http://kb.mozillazine.org/Editing_configuration

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)

• Create the chrome folder (lowercase) in the <xxxxxxxx>.default profile folder if this folder doesn't exist
• Use a plain text editor like Notepad to create a (new) userContent.css file in the chrome folder (file name is case sensitive)
• Paste the code in the userContent.css file in the editor window
• Make sure that you select "All files" and not "Text files" when you save the file via "Save file as" in the text editor as userContent.css. Otherwise Windows may add a hidden .txt file extension and you end up with a not working userContent.css.txt file