I can give you a vague answer.
If using NoScript, allow yahoo.com and yimg.com
If it still doesn't work, then try IE Tab
After you install IE Tab and restart Mozilla Firefox, go to Yahoo's mail page. right click on the Firefox icon at the bottom of the page and click add, apply and ok.
Yahoo will open using the IE tab feature, which is the same as using Internet Explorer.
Hope this helps.
I have lost the ability, in the last 3 days sometime, to download a .wav attachment from yahoo mail while running Firefox (184.108.40.206). Download works fine in IE7 for the same file. This is how I receive my voicemail from my voIP phone service. The only program I knowingly updated in this time is OpenOffice from 2.2 to 2.3
I've tried re-associating the file handling from VLC player to Windows media player to Quicktime and back again - no difference.
Other attachments that I've tried are fine. Any thoughts? Thanks