Why firefox behaves strangely?
 

I used to visit sites to get download music , and uses downloadhelper addons effectively
But while certain mp3 files cant get downloaded , it shows , "following ip already downloading a file ". But my download list is empty
I can download certain mp3 files , but not others , why this occurs?

You don't say anything about your environment, or what version/distro of Linux or Firefox you're using, or what site(s) you're hitting, so it's hard to say.

Chances are, you've got another download running (say, in another tab? Another process?), and that's why you're getting that message.

Ooops sorry , i'm using Ubuntu 8.10 .
I was trying to download a file from a site called 123musiq.com yesterday , for certain reasons i need to stop that , and started fresh today .

When i clicked the same file again i cant download , instead its redirecting to a page telling
"Your IP address is already downloading a file. Please wait until the download is completed."

But i can download other files except what ever i was trying for the previous day

Is this a problem of that site , or firefox downloadhelper addons???

Could be both. Or it could be that as soon as you fired your browser back up again, the session restarted in the background.