hello, it looks like a library called sprotector.dll (which usually resides in %PROGRAMFILES%\SProtector\) is triggering the crashes. do you know of which program it's a part of? this crash is currently investigated in bug #785940.
bug 785940 - Firefox startup crash in _open with SProtector.dll (Safend Protector or Sophos SafeGuard?)
Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.