Update: AIIMS has updated their website to make it more compatible to modern day browsers like firefox and safari. So this post is obsolete now regarding access of that site. But you can use this method to access any site that allow only a specific set of browsers.
aiimsexams.org is the official exam portal of All India Institute of Medical Science, which also happens to be the nodal agency for conducting AIPGMEE ( All India Medical Post Graduate Entrance Examination). This site is used yearly by millions of students and doctors to apply for various exams including AIPGMEE, AIIMS (for MD/MS/Diploma), MDS, DM/MCh, Nursing courses etc.
Unfortunately this site is one of the rarest sites that differentiate users based on their browser. The site does not allow browsers other than Internet explorer to access its full contents. Even though you could apply for an examination in aiimsexams.org using firefox, you won't be allowed to download the admit card or check the percentage of marks once the results come.
If you try to access aiimsexams.org using a browser other than Internet Explorer, an error will be displayed stating that "Incompatible version of browser found. Its highly recommended to use only IE ( Microsoft Internet Explorer) version 6 or above". The boxes for entering the roll numbers will be grayed out( see the screenshots below). The graying will prevent you from punching the required numbers to the box.
This was a great inconvenience for me as I am a complete linux user. IE was not an option(wine could do it but it makes my system unstable). I had to go to Cafe or get a friend's laptop everytime I needed an access to the site, which, needless to say was frustrating. So I searched for a solution to access Internet explorer only site using firefox and found a good add on.
User Agent Switcher - Download
This is a free add on to firefox. Intall it and change the user agent to Internet Explorer.
Using the user agent switcher firefox will mimic itself as internet explorer and you can access aiimsexams.org without any graying out. Once you are done with aiimsexms.org be sure to reset the user agent to the default (just a precaution thats it).
Below are the screenshots of the same page using the same browser but with a different user agent setting.
These two screen shots are barely 20 seconds apart but you can clearly see the difference in the appearance. The user agent was set to Internet Explorer 8 ( 6 and 7 would also work fine).
With this user agent switcher you can download the admit card for AIPGMEE using Firefox itself.
If you want to see the complete installation guide to user agent switcher. Read How to access internet explorer only site using Firefox