Firefox is capable of appearing as BlackBerry browser. Try downloading the free plugin "User Agent Switcher" (https://addons.mozilla.org/de/firefox/addon/59).

Inside the plugin application (Firefox menu "Tools" > "User agent switcher" > "options"), add a user agent with the following string:

"BlackBerry8800/4.5 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102"

You can custimize this to your BlackBerry's model number and OS version if needed.

Then pick this newly added user agent from the menu ("Tools" > "User agent switcher") and try to open the page you need.