[imp] Firefox login problem - doesn't seem to be cookies

[Computer Tech]

Hi all,

openSUSE 10.3
Apache 2.2.4
Horde 3.1.4
Imp H3 4.1.4
PHP 5.2.5
(all of the above "out of the box" openSUSE, with online updates applied.)

When users log in with Firefox or Mac IE, they're just sent back to the
login page.

Horde is set up so that when a user logs in it goes to Imp (in
<horde>/config/prefs.conf, $_prefs['initial_application']).  

None of the several versions of Firefox I've tried work.  Most flavors of IE
work fine, except from a Mac.  Safari works fine.  I don't have any Netscape
running.
  
I've tried setting firefox to accept cookies from the webmail site, block
cookies from the webmail site, neither works. (did "clear private info"
between tries, making sure cookies were included).

I tried turning cookies off (by setting <horde>/config/conf.php line
$conf['session']['use_only_cookies'] = false;) and the browsers still have
the same behavior.  (again, did "clear private info" between tries, making
sure cookies were included).  I noted the URL did change to include
horde=stringofrandomcharacters.  I also note that Horde is still setting
cookies as well as the URL change.

The horde log shows a successful login to horde, but not the corresponding
successful login to Imp that I see when using IE.
From Firefox: (2.0.0.14)
Jun 09 12:51:08 HORDE [notice] [horde] Login success for ctech [10.1.1.5] to
Horde [on line 90 of "/srv/www/horde/htdocs/web/login.php"]

From IE (7):
Jun 09 13:27:37 HORDE [notice] [horde] Login success for ctech [10.1.1.5] to
Horde [on line 90 of "/srv/www/horde/htdocs/web/login.php"]
Jun 09 13:27:37 HORDE [notice] [imp] Login success for ctech [10.1.1.5] to
{xxx.xxx.xxx.xxx:143} [on line 154 of
"/srv/www/horde/htdocs/web/mail/redirect.php"]

To add to the fun, Firefox DOES work every now and then, maybe 1 time in 12.
I haven't seen a pattern of something that makes it work vs not.

I apologize if I've overlooked something simple in the faq, install or the
several forums I've searched.  I've looked through bunches of stuff (most
repeatedly) and still haven't found anything to point me the right direction
to make this work.

Anybody have other suggestions?

Thanks,

rj