I had the same problem running Windows and found that deactivating the Shockwave Flash plugin seemed to solve the problem.

Excellent. I disbled the Shockwave Flash add-on as you suggested and I can now attach files in Yahoo Mail with Firefox 4. Thanks for helping me with this problem :-)

Perfect! It was so easy to fix. I've had this problems for weeks now, and nobody - not even yahoo support has been able to figure it out. THANKS a lot!!

Hi have this problem and deactivating the Shockwave flash didn't help. Now I can't view any emails that support the flash either.

Same problem, disabled Shockwave Flash 10.33.181.34 and now it will attach files and send them with no problem.

Same problem with Windows and this "work around" does help but its not a fix for me as I require the shockwave plug in to view other web content. Enabling/disabling the plugin also isn't a very practical solution. Obviously, there is an issue with either Firefox, Shockwave or Yahoo. From various other Internet posts it looks more likely that the issue is with Firefox. Has anyone figured out how to get the three to work together and/or is someone working on a fix?

I have the same problem with Firefox 6 and the new Yahoo mail. Not an issue with the old yahoo Classic, and works OK on Chrome or Opera. The Flash workaround seems to solve the issue, but as someone else says it means that you lose out on some other sites. needs to be fixed.

You guys are not going to believe this I figured out the problem it's really dumb...ok here goes the attachment uploader loads seperate so I got to thinking it's a popup so I went to options content and under block pop ups there is an option exceptions click on that and in the box type www.firefox.com and hit allow pow its fixed!!!!! :-)

You don't have to disable anything!!! You guys are not going to believe this I figured out the problem it's really dumb...ok here goes the attachment uploader loads seperate so I got to thinking it's a popup so I went to options content and under block pop ups there is an option exceptions click on that and in the box type www.firefox.com and hit allow pow its fixed!!!!! :-)

Question... Are we all having this problem with Yahoo Mail Classic? Is there anyone who is having this problem with Mail Plus? Or any other forms of Yahoo Mail?

i had this problem, after firefox installed its update (without asking me) when i open my yahoo mail, and tried to reply to an email the yahoo account would freeze up, after research i think i found the solution, go to add-ons, look for an add on named browser plus from yahoo, disable this, i did and now it works fine