Hi phylo44,

You should take a look at this Knowledge Base article on customizing the toolbar. It will show you how to add that button back in.

Another possibility is that an addon has been updated and cause the button to move. I know the recent update to Firebug moved the + icon to the side of the toolbar. You can try starting Firefox in Safe Mode by holding down shift while it is starting. If it works after you have disabled all your addons and themes, you can start turning them back on one by one until you find the culprit.

Hopefully this helps!

I found the New Tab button on the side of toolbar (don't know how it got there) and followed your suggestion to use Customize Toolbar. I dragged the icon to the customization page from the side of the toolbar and then from there to the tab itself. It worked. Thanks