I would try to close and restart Firefox because that option should still be there. It is for me at least.

There is a simple way to try and fix the Issue.

Try Resetting Your Toolbar to Default and Resize.

You can always restore the default toolbar settings by clicking Restore Default Set in the Customize Toolbar window.

For more step by step way of fixing the Toolbar Arrangement, Look at this Link

Also Right click on the empty space next to your tabs. Then click customize. It'll be the second one in the list called flexible space. Click and drag it to the toolbar.

didnt work for me!

this solved the problem - many thanks!

this didn't work. The flexible spaces appeared to be put in position but when I clicked "done" they disappeared. Thanks anyway for your reply.

What I did was this; I added a new toolbar, and moved the search window and other things to it. Now I have LOTS OF ROOM

Thanks for your help this was in fact my solution

This problem is new again with FF 29. Now, there is no option to add a "space" at the end of the address bar, essentially making it smaller.

Locking this older thread. The problem being discussed here is different than what is happening with Firefox 29.