gnome3
As of Gnome 3.6, Files (previously known as Nautilus) removes its title bar when maximized. Several other Gnome apps that I generally don't use also do this, e.g. Epiphany.
Is there a way I can stop them from doing this, so that when I maximize an app, it would still have a title bar?
Try the GNOME shell extension TopIcons. This moves the legacy tray icons shown in this bar to the main GNOME bar, up in the top right by the menu.
Simply run this command from a terminal:
gsettings set org.gnome.shell.app-switcher current-workspace-only true
With newer versions of Gnome, this is a configurable setting so installing additional software is no longer necessary.
Best Answer
I found that a preference "ignore-request-hide-titlebar" was added in 3.6. Unfortunately the preference is not loaded from gsettings, so I wrote an extension to set it: https://github.com/garyvdm/gnome_shell_ignore_request_hide_titlebar