Fixing the mailto: problem in Firefox and Yahoo Mail

I was recently helping someone (using Ubuntu 9 on a laptop, which works great, after having switched from XP, which was having registry corruption, even after a wipe/reload), and one of the final cleanup issues was a problem he was having with Firefox and clicking mail links on web pages... the problem is that Yahoo Mail would display the full code of the mailto link in the TO: field, such as mailto:address@isp.com, or if the subject was specified in the link: mailto:address@isp.com?subject=ThisIsTheSubject and he'd have to clean it up before he could send. I finally found a mention somewhere that this happens when the person was using the old version of Yahoo Mail. I was able to reproduce both the problem and the solution on my computer. Switching to the "new" Yahoo email is the answer.