hello, disable the logging: http://support.microsoft.com/kb/161426/en

How i can to do it Windows 7 not have HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tracing

ok sorry, for your OS the path where these settings are determined might be HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing\firefox_RASAPI32

if the "enable"-preferences are set to 1 you might want to turn them to 0. i've attached a screenshot on how it looks for me without having done modifications.

Thank you change EnableFileTracing=1 to 0 and delete firefox_RASAPI32.LOG.