This is a little tutorial that should help you to set up Firefox for using Ultrasurf as Proxy. It should work on Windows as well as on Linux with either Ultrasurf running simply in Wine or as a daemon with ghostship. I will assume that you have already installed Ultrasurf (for detailed instructions on how to do that with wine, look here).
tl;dr: Server: 127.0.0.1, Port: 9666
1. Start Ultrasurf (or ghostship) for the first time. If you use ghostship, read on at step 6 (or if you require that Ultrasurf uses a proxy itself, run ghostship --viewer and follow the next steps).
2. The main interface appears now. Click Option (which should actually be named Options, but that does not matter – the software works anyway 
).
3. Again, you will get another dialog right in your face. This time, check Do not use IE because we are talking about Firefox and not Internet Explorer and Hide Golden Lock because the image of a golden lock at the bottom right is not useful anymore (it should tell whether Ultrasurf has set the IE to use it or not).
4. Optionally, you can make Ultrasurf itself use a proxy by clicking Proxy Settings. This is only required if you can’t access the Internet without using a proxy in your local network or if you want to chain multiple proxy applications in a row.
5. Close the Options GUI (picture above) by clicking OK and the main window by clicking Exit. Then start Ultrasurf again, just as in step 1.
6. Start up Firefox, navigate to checkip.dyndns.org and write down your current IP somewhere.
7. Now you should think about whether you would like to always use Ultrasurf (easier, continue with step 12) or depending on a white- or blacklist with specific sites (read on) and/or with a icon in Firefox that allows easy switching on the fly.
8. Install the Firefox Add-On FoxyProxy by opening this website and clicking Add to Firefox as well as in the popping up dialog on Install Now.
9. Restart Firefox.
10. After that, you will be greeted with a dialog that asks whether you would like to set up FoxyProxy for usage with TOR. In this tutorial, you don’t need to do this as the onion router is a completely different proxy application and should therefore click on No, but you might want to do it anyway if you have TOR installed.
11. Foxyproxy is a very powerful application that allows – as mentioned before – the usage of proxys depending on lists just to name one big feature. Keep in mind that Ultrasurf will listen on your loopback IP, which is always 127.0.0.1 (that information might also be called server), on the port 9666. You can now either do a very simple setup that allows you to switch proxys on the fly by following this tutorial, or dive right into the official FoxyProxy documentation and learn how to use the more advanced features. Continue when you have Ultrasurf set up.
12. Open up Firefox’ preferences by clicking Edit/Preferences (Windows users will find it in the Tools menu).
13. Navigate to Advanced, Network and set up a pretty high cache, like in the screenshot below (1024 MB). This will make sure that Firefox downloads only new data and keeps the old on the harddrive, thus speeding up the surfing experience and keeping away unnecessary traffic from Ultrasurf.
14. If you use FoxyProxy, click Close and continue with step 16 now. otherwise click Settings.
15. In the new GUI, click Manual proxy configuration, Use this proxy server for all protocols and fill in the following data:
HTTP Proxy: 127.0.0.1
Port: 9666
After that, click OK.
16. So you set everything up? You better check that by calling checkip.dyndns.org again and comparing the current displayed IP with the one from step 6. If it is different, everything works 
