This I had learned from CibaiPukimak
All credits goes to him. I'm just translate and share it in English version.

This is only for beginner, maybe some of you know many more ways than this way.

Okay, I will tell you how to play on multiple account without any add-on.

First, you need to learn the basic, "The servers".
Thecrims has 10 servers right?
So what will you do with this?

Go to address bar, and type
Code:
www1.thecrims.com or 
www*.thecrims.com
fill the * with number from 1 - 10
then login with this address.

Why I don't use www.thecrims.com? Because when you login from this address you will be given random server.

You've got the first step now.
The first step only teach you how to login with 10 account, so what about login in more than 10 account?

Second, go to desktop and find your Firefox shortcut, click on properties and replace or change the target with
Code:
"C:\Program Files\Mozilla Firefox\firefox.exe" -p -no-remote
Once you done, click apply and then OK. Open Firefox from your shortcut, you will redirected to Firefox manage profile. Every profile give you different cookies,

If you wanna play with 23 account so you need 3 Firefox profile.

I haven't tried it yet. But I'm sure this way will work 80%.

Happy playing criminals.