Text disappears when using modify,preview or quote

One of my users is having a problem with modifying their post. What happens is that the text box appears empty and they have to copy and paste their text from the thread and then make modifications.She also cannot use preview button as everything she typed disappears. And she hasn't been able to use quote button.
Her browser is MozillaFirefox and has had the problem for about a month.
She cleared her cache and it didn't help.

Has she tried a different browser just to see if it still dose it.
I was thinking may be she has her advanced editor on, but that would not explain the quote and preview.

So it's hard to say right now, ask if she can get a screen shot.If you can open a test forum for guest to post so we can go there and see if it happens to us as well..