You can find the New Tab button showing as a '+' on the Tab bar.

You can open the Customize window and drag the New Tab button that shows as a plus sign (+) from the Tab bar on another toolbar and it will become a regular toolbar button like the New Tab button that you have in Firefox 3 versions.

If you can't find the New Tab button then click the "Restore Default Set" button in the Customize window.
If you want the New Tab button at the far right end of the Tab bar then place a flexible space to the left of it.

Open the Customize window via "View > Toolbars > Customize" or via "Firefox > Options > Toolbar Layout"

• https://support.mozilla.com/kb/Back+and+forward+or+other+toolbar+items+are+missing

• New tab toolbar button: https://addons.mozilla.org/firefox/addon/new-tab-toolbar-button/

there is no new tab button or + sign in the customize window even after restore defaults - this is firefox 6.01 - CTRL-T still works

Are you using a custom theme?
In that case you may be using a theme that doesn't support that New Tab button.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

See also:

• https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

• http://kb.mozillazine.org/Corrupt_localstore.rdf