Hi Baris,
I am not familiar with Safari but the following info might be helpful for you;
On FF by default the SSO is turned off. so you do not get the certificate prompt.
On IE, the SSO can be turned off as follows:
Tools > Internet options > Security > Custom Level > Miscellaneous > Dont prompt for client certificate selection when no certificate exists.
I am sure that Safari has a similar setting (google it...)
Resetting your safari back to it's default settings should also resolve this issue.