1. Open omni.jar and remove these lines (1989 - 2004 for 4.0b6pre linux) from chrome/browser/content/browser/browser.xul:

     <statusbarpanel id="sync-status-button"
                     class="statusbarpanel-iconic"
                     image="chrome://browser/skin/sync-16.png"
                     label="&syncLogInItem.label;"
                     oncommand="gSyncUI.handleStatusbarButton();"
                     onmousedown="event.preventDefault();">
     </statusbarpanel>
     <separator class="thin"/>
     <statusbarpanel id="sync-notifications-button"
                     class="statusbarpanel-iconic-text"
                     hidden="true"
                     popup="sync-notifications-panel">
     </statusbarpanel>
     <panel id="sync-notifications-panel" position="before_end">
         <notificationbox id="sync-notifications-box"/>
     </panel>

2. Remove XUL.mfasl.

Add this to the userChrome.css file to block Sync from having anything appear on the Statusbar.
http://kb.mozillazine.org/UserChrome.css

#sync-status-button { display: none !important; }

#sync-notifications-button { display: none !important; }