Mozilla's tab preferences have an option named:
[x] Hide the tab bar when only one tab is open.
It defaults to being enabled as above, however if you clear the
checkbox, thus disabling the preference, quit mozilla and start
it back up again, mozilla starts up with your default page in a
browser window, with no visible tab bar. It ignores the
preference at startup time essentially. Once you have opened a
new tab up, either by clicking on "File->New-New browser tab" or
hitting CTRL-T, the tab bar appears and stays there as expected.
FC1 mozilla-1.4.1-18 (however all versions of mozilla seem to do this)
When the above preference is turned off, the browser should start
up with a visible tab bar right away, and open the default page
in the first tab. This allows you to use the right click tabbar
menu to open new tabs, close them, etc.
This was fixed at some point. Certainly works for me on 1.7.12