By default the tab strip is now on top. The button to open tabs is then on the same level.

Also note there are other methods of opening newtabs for instance the Keyboard shortcut Ctrl+T

• Keyboard shortcuts - Perform common Firefox tasks quickly_windows-tabs

You did not provide full troubleshooting information so we do not know exactly what you may have changed.

I am sure with addons you could move the tabs bar and the open tabs button if you find that important.

• Have a look at this thread
  Can tabs still be place under the address bar? i used the browser.tabs.onTop fix /questions/985773
• Try using this addon
  Classic Theme Restorer:
  https://addons.mozilla.org/firefox/addon/classicthemerestorer/
• Or this for an even older look
  Firefox 2, the theme, reloaded 1.0.7
  https://addons.mozilla.org/firefox/addon/firefox-2-theme-for-firefox-3x/

What I'm trying to say is: in Firefox 29.0.1, the Open New Tab feature no longer appears as a Tab on the Tab Strip, to the right of other Tabs. Open New Tab is now a toolbar button. I want it as a Tab again.

Delete the localstore.rdf file in the profile folder and restart firefox.

NOTE: This will reset the toolbar configuration (where you have placed buttons at)

If you need help finding your profile folder refer to the Profiles - Where Firefox stores your bookmarks, passwords and other user data article.

You can open the customize window and drag the new tab button to the tab bar between the last tab and the list all tabs button.

If that doesn't work then click the "Restore Defaults" button.

• 3-bar Firefox menu button > Customize > Show/Hide Toolbars
• View > Toolbars > Customize (press F10 to show the Menu bar)

Dragging only moves New Tab over to the extreme right of the Tab Strip, making it a button marked with a +. That's an annoying place to have it.

You have not told us what addons and customisations you initially had. Or what addons you have since tried.

A screenshot of the original setup may have helped, but it is hardly now worth going to all the trouble of an additional custom install of an old version of Firefox to demonstrate that and provide a screenshot.

A screenshot of the current setup and problem may still be helpful, in aiding our understanding of what you are seeing and attempting to do

• How do I create a screenshot of my problem?

"Dragging only moves New Tab over to the extreme right of the Tab Strip, making it a button marked with a +."

Yes, I have had that happen myself, when I had "too many" tabs open already when I opened "Customize Firefox" which opens in a new tab.

Please try moving that "open new tab" to the tab strip when only the "Customize Firefox" tab is open and make sure you drop it right next to that one tab. It seems that button can be cantankerous when moving it at times.