Alt O for the options. On the left, a few boxes down, uncheck the box for tells to pop up a new window or w/e.. should be back to somewhat normal..
Folks have posted UI modes to disable it. Its fairly easy to do. Down the mod, throw it in as part of a custom UI set, reload.
The height of the chat tab is twice that of the title bar. Removing the title bar itself isn't a full fix.
Using the ui mode that removes tabs is a full fix. Works very nicely. Took maybe 10 min to undo the tabs.