I use Firefox on two ubuntu systems 9.04 and 9.10 and never
had this problem.

edit/preferences/main and you will find it.

I have used Firefox on Ubuntu for several years now on at least a dozen
different machines. This is the first time I have encountered this problem. I
attempt your solution every time that I bring up Firefox, and it only works for
that session. That is why I am asking for the name of the file that Firefox uses
to store preferences. I just recalled that when I run sudo firefox from a
command line, it starts correctly. This should be telling me something, but I am
not sure what! I suspect that either I have two properties files, or that
somehow the permissions have changed.

its under edit.

I have that as one problem with FF 3.5 you do not mention which
version you are running.

I am running Firefox for Ubuntu version 3.0.14.
I know how to find the GUI interface to the properties file in the menu, I just
don't know where the file itself is hidden.

Are you comfortable with the command line? If so, look in your home for
a directory called .mozilla, and you will everything firefox related is
under that. Do a long listing and make sure that you, not root, own all
the files.

It's in .mozilla/firefox/uniquenametoyoursystem.default
just open a terminal and cd to .mozilla/firefox then ls to find your
default profile folder.

Its in the Edit Menu.........................