@jimjams91this is much in line with IE9 - IE11. But it eats a lot of space that is now used for displaying tabs.
As such i would prefer an approach more in line with the Min browser ( https://minbrowser.org ) or the most recent safari version (only available upon manual activation).
As a compact mode, Firefox would look like this:
Now, where do you put URL or make a search? Well, when you Double Click a tab or press Ctrl+L it would focus and show the URL bar (Esc or Enter gets you back to tabs):
But this should always be a "compact mode", and not the default GUI.
This is a fantastic idea. It could be a tiny widget on the tab bar or even only a button, such as the rest of the buttons. Screen real estate is the best!