Opening a .eml file depends on the email software that you use. For instance, Internet Explorer can now open .eml files since they are basically formatted in the same manner as .mht files are. Simply change the filename extension from .eml to .mht, and the file can now be opened on Internet Explorer. If you have Outlook, simply click the file and it should open easily in the program. If Outlook is not your default application that opens .eml files, simply right-click on the file, choose Open With and then select Outlook Express. Using Windows Mail, simply drag and drop the .eml file into one of your folders and click on it to open it.or u can use a FIREFOX EML file viewer software .

AFAIK Firefox didn't handle .eml before. So your link of a software like Firefox to a file extension like .eml may be wrong (Windows).

Why not use Thunderbird though, also from Mozilla. Probably the obvious choice, if you already have Firefox, rather than arguably worse options like Outlook (Express).