[Sage-4.7]SageNB returns no result

edit

As a new sage user, I recently compiled Sage-4.7 from source and it runs smoothly in the command line. However, when I set up the sage notebook, the expression returns no result in browser For instance, if you enter 1+1, then click "Evaluate", the cell turns green but then it keeps running and never returns anything. The terminal displays the following:

sage: notebook(interface='', server_pool=['sage1@localhost'],                 
....: ulimit='-v 500000', secure=True, directory="/tmp/work", accounts=True)  
The notebook files are stored in: work.sagenb                                 
****************************************************                          
*                                                  *                          
* Open your web browser to https://localhost:8000  *                          
*                                                  *                          
****************************************************                          
There is an admin account.  If you do not remember the password,              
quit the notebook and type notebook(reset=True).                              
/tmp/work/sage-4.7/local/bin/sage-native-execute: line 8: firefox: command not
 found                                                                        
2011-06-20 13:50:09-0400 [-] Log opened.                                      
2011-06-20 13:50:09-0400 [-] twistd 9.0.0 (/tmp/work/sage-4.7/local/bin/python
 2.6.4) starting up.                                                          
2011-06-20 13:50:09-0400 [-] reactor class: twisted.internet.selectreactor.Sel
ectReactor.                                                                   
2011-06-20 13:50:09-0400 [-] twisted.web2.channel.http.HTTPFactory starting on
 8000                                                                         
2011-06-20 13:50:09-0400 [-] Starting factory <twisted.web2.channel.http.HTTPF
actory instance at 0x19ef35a8>

I tried checking the installation using make check and it is fine. Can someone give me some ideas on how to proceed?

Thanks so much!

Riemann