I have read the FAQ entry as well as all of the forum discussions that talk about problems with the visual editor not working, and I've followed all of the suggestions and instructions, but on the two computers I use at my workplace the visual editor is still not working.
On both computers I'm using Firefox 1.0.7 (I know, I know). The OS for both computers is Windows 98 (I know, I know). I have repeatedly cleared the browser cache, checked and unchecked the "use visual editor" option on the Users:Profile page, restarted both computers, and checked to see if there's a problematic browser extension factoring into the mix (which isn't the case). And yet the problem remains the same: on both of the computers I use at my workplace -- which is a public school where all computers are on a LAN with a high speed Internet connection (I'm not sure exactly what type) -- the visual editor spontaneously stopped working a little over a week ago.
One interesting thing I have noticed is that when I'm on the "Write Post" page looking at all of the HTML code where the visual editor should be in action, the visual editor option still looks like it's selected. But none of the formatting buttons appear. And if I click the html option, this makes the field for typing text completely disappear, after which there's no response when I click the visual editor option. I have to navigate away from the page and then return in order to bring up the typing field again, at which point the same problem is in effect: no visual editor.
FYI, at home I use Firefox (I forget which version but I think it's newer than what I use at work) on two separate computers with Windows XP and have experienced no problems and no change in the visual editor experience.