Trying a repost as I fear I chose the wrong forum this morning. First I want to say that any advice you give me (for which I am extremely thankful) - should be as if you are explaining them to your grandma. Because I am only slightly more familiar with this than she is.
I am using the "platform" free theme from pagelines but in googling I see many people with the same issue using other themes too. The site in development stage is seedprograms.org/build.
The dropdown menus disappear on your way down with your cursor, sometimes. This appears as "flickering" or jumpiness. You are more likely to see this if you zoom in on the browser because the area that creates a problem if your cursor hits it is only a small number of pixels, maybe 1.
Not in IE. I think there is some kind of fix in place for IE that essentially breaks things in firefox and chrome. Just a theory. Again, seedprograms.org/build - try any dropdown menu.
The diagnosis I have done by using the "inspect" function in Firefox and causing the problem in slow motion is this:
-when your cursor moves from the main nav down toward the dropdowns, the problem arises when it hits an area called div#nav_row.main_nav.fix along the way.
When you hit this area and continue downward, your connection to menu navigation has been broken and you end up in div.mcolumn-pad with the dropdown having disappeared.
The dropdowns are already position: relative with a z-index of 28.
I have really not customized anything that should impact this layout.
On the pagelines forum the main thing the experts say when somebody has this problem is, disable all your plugins and see if that fixes it and if so bring them back one by one.
I have done this and it didn't help.