I'd be surprised if you could open them on Firefox. An EML file is an archived email that preserves the original HTML formatting and headers. Most mail clients support EML files, but if you don't have an email client installed, or are using a mobile device, there are workarounds you can use to open the file. This file type is supported by Microsoft Outlook / Outlook Express. Firefox cannot display these natively. You can try two things. * To open the .eml in Firefox, change the .eml extension to .mht * Open the .eml in Outlook. Note: If you use Windows Live Mail Some users have reported that backups created with Windows Live Mail have corrupted EML extensions (*._eml instead of *.eml). If the EML file isn't opening, check that the extension is not messed up.