My dad's computer is running OS X 10.5.8, and is almost always unable to open secure web pages from his account. It's not that he can't log in—it's that the servers never even send a reply. This is true from Safari 5.0.6, Firefox 12.0, SeaMonkey 2.13.1, and telnet to port 443. All three browsers report that they are unable to establish a secure connection to the requested website.
But when I'm logged into his machine on my own account with those very same browsers, I can get to secure pages without any problem, and web browsing in general seems to be faster from my account than his.
I've reset Safari for his account, but that made no difference. We've restarted the machine multiple times. His account is not an administrator account and I have parental controls enabled for him to keep him from accidentally modifying his Dock. I've checked for suspicious-looking processes but haven't seen any red flags. If I enable the Web Console in Firefox, it posts the following and nothing else. I have observed this behavior for multiple sites, and over a period of a month or more.
[23:51:21.335] GET https://www.bankofamerica.com/ [undefined 78ms]
I observe all of this while VNC'ed into his machine with Screen Sharing. What could possibly explain this kind of difference in browser behavior between his account and mine?