If you like your tabs on the bottom - below the toolbars - instead of on top, here is the simple solution. This works with the new Firefox version 29.0.1.
You may have had your tabs below the toolbars up until now, and then Mozilla updated Firefox to version 29.0.1
If you want your tabs back below the toolbars, download and install Classic Theme Restorer. Restart Firefox. Then open the Add-ons page, go to Extensions, then click on Options for Classic Theme Restorer. Change Tabs On Top to Tabs Not On Top. OK. Done.
I found that manually making the change in About:config did not work, but this add-on does.
There are a lot of other things you can do with this add-on. See this page for more about this add-on.