Once associating a file type to "Open with" a particular program, do you need to restart Firefox for the change to take affect?
Once I've downloaded an unassociated file type, Firefox asks what to do with the file. I choose "Open With" and select the program I'd like Firefox to use to open the file and the file opens correctly.
With out closing Firefox, I try the same file again, I'm prompted to choose what to do with the file again. Do I need to restart Firefox or clear cache for the file type association to take place?
Additional question, will Firefox use file type program associations already set in Windows?
Opaite Mbohovái (2)
You need to make sure that you check off the Do this automatically for files like this from now on option on the popup window that appears when you try to save the file.
You can also try setting the default behavior for Firefox using the applications panel.
However, if the file has never been opened from your operating system before, it's possible that it doesn't have a default program set for that file type. This could mean that you are seeing the "Open with" popup from your operating system, not with Firefox.
If that's the case, you need to set the default program within your operating system. The How to Set Default Programs in Windows 8 page on WIkiHow has more information on that.
jjm552 said
Additional question, will Firefox use file type program associations already set in Windows?
Usually if you have not specified some other program to handle a particular content type, Firefox will show the default handler in Windows.
But note that I said content type which is information the server provides along with the download. Firefox does not typically rely on the file extension or file contents to identify the program to handle a particular download. If the server is not providing an appropriate content type with the download, Firefox may treat it as a one-off and not treat future downloads the same way.