As a temporary workaround, you should be able to use one of these methods to open a new tab:

• Ctrl+t
• (menu bar) File > New Tab
  If you do not display the classic menu bar full time, tap the Alt key or F10 function key to activate it
• right-click Windows 7 Taskbar icon > Open new tab

As for where it went, hmm, if this wasn't the result of a new add-on or updated add-on, you may need to go into the Customize mode to look for a misplaced "+" button, or use the Restore Defaults button at the bottom of the Customize tab to reset toolbars back to their original layout. More info: Customize Firefox controls, buttons and toolbars.

Any progress?

Thank you! The first option worked! Later I will see about resetting toolbars back to their original layout. I am MOST appreciative!

Yes! I restored defaults and the PLUS came back! Thank you JScher!!!

Great news, thanks for reporting back.

J, Please tell me how to restore my toolbar Bookmarks. I can bring them up but only temporarily. I want them permanently there like they were before. Thank you J! I may have to recreate them, but am lazy! gina

Hi Gina, to turn different bars on and off, you can use one of these methods to show the toolbar list and select the desired bars there:

• right-click a blank spot on the tab bar (or the "+" button)
• tap the Alt key to activate the classic menu bar > View > Toolbars
• in Customize mode > Show/Hide Toolbars (see: Customize Firefox controls, buttons and toolbars)

To turn on the Bookmarks Toolbar, Menu Bar, or other bars, click it on the list. Or "uncheck" them to turn them off.

Dear J, THANK YOU! I was there but didn't look down to see the show/hide option. Much appreciated! gina