Can't comfirm the tab behavior. Is the menu item (File>New Tab ⌘T) greyed out for you? Do you use a langpack other than English (some localizations have different menu shortcuts)? What happens when you right-click on a link and choose Open Link in New Tab? Any add-ons that might cause this?
I have same problem - no tabs neither contexual new tab nor using file>new tab (menu item not greyed out). Only new window option works by using contextual open in new window
Also no toolbar visible even though selected in menu. All menu items dont work either.
up/down scroll arrows dont work either.
Disabled all add-ons with no improvement.
There must be some weird settings left over, stuck in your preferences, maybe even from an add-on that has long been removed. The only advice I can offer here is to reset your user profile. Go to Help>Troubleshooting Information and click Refresh TenFourFox.