clear the history/cache from your the browsers then recheck it.

The best method to check the ranking of your site is you just check the position before starting any other work.If you are opening your account which you are using for your posting job, the result will vary.So, close all the windows.Open a browser and check the ranking and then you can open your account.

hhmmm.. this problem is also i am too facing ... Thank you for your kind reply ..

whenever u need to go for ranking check plz clear history of your browser and then try it.

I agree with stunning boy .
If you are using Microsoft Internet Explorer 8.0. Then you can follow the following steps to clear browser cache.

1. Open Internet Explorer and select the Tools icon.
2. Select Internet Options and choose the General tab.
3. Select Delete under "Browsing History".
4. Select Delete Files under "Temporary Internet Files".
5. Select Yes on the Delete Files dialog box.
6. Select Close and then OK.

I tried all these methods but not same ranking on FF, IE , CHROME . 

It's conman issue.. May be you are login into any Google services like Google+, gmail, blogspot etc. check . Clear you browser history, sign out if you are login in any A/C.. If problem is still after apply these method you can restart your machine. maybe it will help you.

I think this not a bid problem just clear your browsing history and check once again you ranking.