Clicking the "collapse" control on the menu toolbar in the Address Book causes the toolbar to collapse, but clicking the control again doesn't restore the menu toolbar. The Mail Toolbar works fine. Mozilla 0.6 Windows NT 4.0, SP5
Works okay for me using dec12 commercial trunk build win98.
Verified as worksforme on win32, linux, and macos using the following builds: win32 commercial seamonkey build 2000-121809-mtrunk installed on P500 Win98 linux commercial seamonkey build 2000-121808-mtrunk installed on P200 RedHat 6.2 macos commercial seamonkey build 2000-121808-mtrunk installed on G3/400 OS 9.04