Here I have Created a simple tutorial to show you how to login with Multiple Orkut/Gmail or Yahoo Id at the same time using Firefox Browser.
This is simple hack that you will love to do if you are a Firefox Lover.By doing this you can login with Multiple Ids for any mail service.So Here we go,
1.Right Click on My Computer-->Properties-->Choose Advanced Tab.
2.Click Environment variables button.Under System Variables section, Click new.
3.Now type this information to each textbox.variable name: moz_no_remotevariable value: 1
4.Press ok.
5.Now Right Click Firefox icon in desktop Select Properties.
6.Add extension -p to command line(like "c:\program files\mozilla firefox\firefox.exe" -p).As i have shown in the below screenshot,
7.Press ok.
8.Now Open the Firefox it will ask for Choose Profile.
9.Now you can Create a new Profile by clicking Create Profile Button.
10.After Creating a Profile,select any one Profile for using Firefox.
11.So by selecting Other Profile you can simultaneously login to two accounts of any(orkut,yahoo,rediff or anything else)
Note:You can increase you Create more Profiles for accessing more than 2 account