One way is to use this macro
_command void show_current_buffer_in_browser() name_info(','VSARG2_REQUIRES_MDI_EDITORCTL|VSARG2_READ_ONLY)
{
safe_goto_url(p_buf_name);
}
add the code to the vusrmacs.e file in your configuration folder. If you don't have a vusrmacs.e file, record a trivial macro and save it and vusrmacs.e should be created. To load the macro, open vusrmacs.e in the editor and use the load module command on the macro menu. Then you can bind a key to the macro or you can add it to the right click menu in the editor - to do that, right click in the editor window and select "edit this menu". You are then presented with the menu editor. Click the help button for some help. The name of the right click menu is "_ext_menu_default". To add your command, first you need to select the position in the menu that you want it to appear - using the edit window with the scroll bar at the bottom of the dialog. In the "command" field you need to enter the name of the macro show_current_buffer_in_browser, and put something suitable in the caption. Then click one of the buttons "insert after" or "insert before".
Another way is to use the shell command - look up shell in the help. e.g.
shell("man cc","","xterm -T "man" -e /bin/sh -c");
or
shell('"C:\Program Files (x86)\Google\Chrome\Application\chrome.exe" ' :+ maybe_quote_filename(p_buf_name));
Also, in tools -> options, search for "browser" and see how to select a default browser.