Hi,

Please check if this happens in a new profile. If the new profile is okay, you can then Reset Firefox on the old (previous) profile via Help (Alt + H) > Troubleshooting Information.

Looks like a problem with floating content and a missing clear rule.

Something like this seems to work.

UL.menu > LI { clear:both; }

where should i add it.

If you have access to the template_css.css file then you can add that rule to that file.

ul {
  float            : left;
  margin           : 2px;
  list-style       : none;
}
li {
  padding-left     : 0px;
  padding-top      : 0px;
  line-height      : 25px;
  border-left      : 5px solid #fff;
  clear            : both;
}