Firefox recently implemented font downloading, but the possible formats are limited. That site has a style rule pointing to a .eot file (Embedded OpenType) which is a legacy format that wasn't implemented in Firefox. This page has information about Firefox's support for @font-face: https://developer.mozilla.org/en/css/@font-face

I did a search for alternate sites where you could download the SutonnyMJ font in TrueType format, and found these. No way for me to verify that the files are safe, you'll have to make your own judgment and trust your antivirus software.

http://bangla-sydney.com/message_bangla_download.asp
http://www.khamarbd.com/font.htm
http://www.itservicebd.com/bangla_service/bangla_font_install.htm
http://www.kmcbd.org/Home/documents

Edit: I see you already have the .ttf file, so you won't need those links!

thanks for your reply.though i solved the problem but i am asking where is such settings "in IE tools->internet options->security->custom level->Downloads->font download->enable".

in FireFox

It is enabled by default. If you wanted to disable it, I believe the setting is gfx.downloadable_fonts.enabled (you can adjust this value using the about:config preferences page).