Richard,
There are at least 4 different solutions (maybe more, the 10 page thread is very confusing, especially as people are not always specific about which CSS file they are updating).
None of the suggestions I was able to identify clearly and implement have made the menus in Firefox behave correctly. The most recent suggestion is from April 2013, most of the thread came from 2011-2012, and I have an awful feeling that the files involved have changed since then. (For instance one guy said, "The
problem we've found with every install of DNN 6 and menu issues is
line 231 in the default.css. Take all the content out of .DnnModule
and upload. Should read .DnnModule {} after editing." So I looked in that file, and line 231 in DNN 6.2.8 doesn't contain the .DnnModule statement at all.
Can someone please tell me how to fix this with the 6.2.8 version of DNN? I can't put it in production if it doesn't work in FireFox. There's a lot of discussion of z-indexes; there are z-index statements all over the default.css for 6.2.8, and I have no idea what they do, not being a skin expert. I've checked the CSS files for my skin and none of them has any z-index statements at all.
Should I just find the .DnnModule statement and remove everything from the braces? (It's on line 258.) The poster in 2013 (see p.10) suggested removing only the "zoom:1;" statement from that line, which I tried. It didn't work. "Didn't work" means that I changed the file on my site, restarted the application on the Host Settings panel, and reloaded the page in FireFox, with no change in the menu behavior.