1. Log in to your facebook account with your phone (as usual you'll be redirected to the mobilesite. Don't worry). Now, Navigate/Open your profile/timeline page located besides the home tab. It will look somewhat like this -

2. Now navigate to the bottom of the page and click log out option -

3. A normal facebook log in page will appear..

4.
Note- (This step is very Important) Now just simply go back by clicking on back button or by pressing right hand soft key of your mobile to open the cached copy of your profile page and
again click on the log out link [important]!!!
5. Now a facebook login page with an error message (you must login first) appears.. [shown below]-

6. Now enter your account details in this page and click Log In.. Thats all...!
[Source: Internet!]