Ok, you mean Firefox is trying to download the VdHCoAppSetup-1.2.4.exe file.
Maybe you once tried to download this file and for some reasons, the download failed, so you now have this entry in the Firefox download history and it stays there as it has not been cleared.
Can you right-click on this entry, pick "Copy Download Link", and paste the URL here ?
Then, right-click again and choose "Remove from history".
Do you get the problem again ?