Firefox 7 can be installed on Linux Mint 11, the same way how we install Firefox 7 on Ubuntu. Just Update the repository and use apt to install it.
For Fedora Click Here.
Run the following commands one by one in the terminal and type the password for the user, when prompted.
To Update the Repository
sudo apt update
The above command will update your system repository.
To Install Firefox 7
sudo apt install firefox
The above command will install the latest version 7.0 in your system.
Thats it. To check the version start your Web Browser and select About Firefox from Help menu. Check the screen shot below.
Hope this will be helpful for you!!!