There isn't a way to find out where it is, but you can disconnect the device from your Firefox Sync account. # Go to '''https://accounts.firefox.com/settings/clients''' and sign in using your Firefox account password. # Beside ''Firefox-iOS-FxA/...'' click on '''Disconnect'''. I might be mistaken, but I think if you use a desktop web browser and log in at https://www.icloud.com/ , you should be able to see your iphone listed in the Settings panel, and click on it for options regarding reporting it and ''maybe ''wiping it. The folks at https://discussions.apple.com/welcome might be able to help.