Macos – Cannot load webpage on one particular computer

I have a computer running OS X 10.6.8. One particular webpage will not load regardless of browser or network. Here are the symptoms:

• The website does not load when the URL is entered into any browser. On Firefox, the error is usually "Connection timed out" but sometimes it is "Unable to connect"
• Changing the DNS server does nothing.
• DNS is resolving the correct address for the page. I checked this with nslookup and compared it to a machine which can successfully load the page.
• Cannot ping the site without timing out
• Flushing the cache in the browser does nothing
• Flushing the cache with dscacheutil does nothing
• Clearing browser cookies does nothing
• I can access the page just fine on other devices connected to the same network
• The webpage does not load regardless of network on the victim machine. I tried using my phone's hotspot and the page still does not load on the victim computer. The page loads just fine on my phone.
• No proxy is being used
• Using a VPN DOES fix the problem
• /etc/hosts is stock
• I did a scan for malware using clamXav. Nothing turned up except for a couple false positives
• Rebooting does not fix the problem
• Booting into safemode DOES fix the problem, but the problem then recurs after booting normally again

I'm really at a loss here. This just started up recently, and I can't recall any change which would have precipitated it.