Nice menus compatability problems with Celju and Shallow Grunge in Firefox

I have found that in both the Celju and Shallow grunge with firefox, the drop down menus do not appear when hovering over the first parent item with children. Instead they only flicker on as the mouse rolls over the borders of the box, but they only briefly appear and then disappear again. When I switch to Bluemarine or use Internet Explorer, the menus work as expected. Here's the site:

http://www.ltneighbor.com/drupal/

I tried looking for overflow:hidden in the theme css as suggested here: http://drupal.org/node/367407 but didn't find it anywhere in the shallow grunge theme. I also used the Firefox Firebug plugin to compare the css from the working menu with the non working menu. Here's what I found when comparing the css for the link inside the menu item (<a title="About Us" href="/drupal/node/66">About Us</a>)

CSS that works:

ul.nice-menu-down .menuparent a {
padding-right:15px;
}
nice_men...ult.css?E (line 181)
ul.nice-menu a {
padding:0.3em 5px;
}
nice_men...ult.css?E (line 62)
ul.nice-menu a {
display:block;
}
nice_menus.css?E (line 26)
a:visited {
color:#336699;
}
style.css?E (line 39)
a {
font-weight:bold;
text-decoration:none;
}
style.css?E (line 32)
Inherited fromli#menu-323.menuparent
ul.nice-menu li {
border-style:none solid solid;
}
nice_men...ult.css?E (line 42)
Inherited fromul#nice-menu-1.nice-menu
ul.nice-menu, ul.nice-menu ul {
list-style-image:none;
list-style-position:outside;
list-style-type:none;
}
nice_men...ult.css?E (line 34)
Inherited fromdiv#block-nice_menus-1.block
.block-nice_menus {
line-height:normal;
}
nice_menus.css?E (line 11)
Inherited fromtable#header
table {
font-size:1em;
}
style.css?E (line 55)
table {
border-collapse:collapse;
}
defaults.css?E (line 21)
Inherited frombody.lightbox-processed
body {
color:#000000;
font-family:Verdana,Arial,Helvetica,sans-serif;
font-size:76%;
font-size-adjust:none;
font-style:normal;
font-variant:normal;
font-weight:normal;
line-height:normal;
}
style.css?E (line 6)
ul.nice-menu-down .menuparent a {
padding-right:15px;
}
nice_men...ult.css?E (line 181)
ul.nice-menu a {
padding:0.3em 5px;
}
nice_men...ult.css?E (line 62)
ul.nice-menu a {
display:block;
}
nice_menus.css?E (line 26)
a:hover {
color:#3399CC;
text-decoration:underline;
}
style.css?E (line 42)
a:visited {
color:#336699;
}
style.css?E (line 39)
a {
font-weight:bold;
text-decoration:none;
}
style.css?E (line 32)
Inherited fromli#menu-323.menuparent
ul.nice-menu li {
border-style:none solid solid;
}
nice_men...ult.css?E (line 42)
Inherited fromul#nice-menu-1.nice-menu
ul.nice-menu, ul.nice-menu ul {
list-style-image:none;
list-style-position:outside;
list-style-type:none;
}
nice_men...ult.css?E (line 34)
Inherited fromdiv#block-nice_menus-1.block
.block-nice_menus {
line-height:normal;
}
nice_menus.css?E (line 11)
Inherited fromtable#header
table {
font-size:1em;
}
style.css?E (line 55)
table {
border-collapse:collapse;
}
defaults.css?E (line 21)
Inherited frombody.lightbox-processed
body {
color:#000000;
font-family:Verdana,Arial,Helvetica,sans-serif;
font-size:76%;
font-size-adjust:none;
font-style:normal;
font-variant:normal;
font-weight:normal;
line-height:normal;
}
style.css?E (line 6)

Non-working CSS:

#menu a {
border:medium none;
color:#FFFFFF;
display:block;
font-family:Arial,Helvetica,sans-serif;
font-size:10px;
font-weight:bold;
padding:13px 10px 10px 20px;
text-decoration:none;
text-transform:uppercase;
}
style.css?E (line 168)
ul.nice-menu-down .menuparent a {
padding-right:15px;
}
nice_men...ult.css?E (line 181)
ul.nice-menu a {
padding:0.3em 5px;
}
nice_men...ult.css?E (line 62)
ul.nice-menu a {
display:block;
}
nice_menus.css?E (line 26)
a {
border-bottom:1px dotted #999999;
color:#A42424;
text-decoration:none;
}
style.css?E (line 42)
Inherited fromli#menu-323.menuparent
ul.nice-menu li {
border-style:none solid solid;
}
nice_men...ult.css?E (line 42)
Inherited fromul#nice-menu-1.nice-menu
#menu ul {
line-height:normal;
list-style-image:none;
list-style-position:outside;
list-style-type:none;
}
style.css?E (line 157)
ul.nice-menu, ul.nice-menu ul {
list-style-image:none;
list-style-position:outside;
list-style-type:none;
}
nice_men...ult.css?E (line 34)
p, ul, ol {
line-height:180%;
}
style.css?E (line 34)
Inherited fromdiv#block-nice_menus-1.block
.block-nice_menus {
line-height:normal;
}
nice_menus.css?E (line 11)
Inherited frombody.lightbox-processed
body {
color:#000000;
font-family:"Trebuchet MS",Arial,Helvetica,sans-serif;
font-size:13px;
}
style.css?E (line 7)