Corporate Firewall Stopping TOR

[Paul Hunt]

I am trying to use tor through a corporate firewall with a proxy address of 
proxy.xxxx.com.  Neither of the folllowing sets of lines in torrc appear to 
enable this.  Obviously, there is something here that I do not understand.  
If you can, please tell me what I am missing.

FascistFirewall 1
FirewallPorts 80
HttpProxy 192.xxx.yyy.zzz

FascistFirewall 1
FirewallPorts 80
HttpProxy proxy.xxx.com

(192.xxx.yyy.zzz is the IP address of proxy.xxx.com.)

Thank you in advance for your help.

Sincerely,
Paul Hunt