dbhutchins, I'm seeing the same on multiple macs.
It seems to have been introduced as far back as updating from 10.9.2 (my personal upgrade path was going from 10.9.2 → 10.9.4 → 10.9.5). The issue occurs on both my macs (one 2011 iMac, one 2012 MacBook Air).
I suspect the issue was introduced system wide in an update released after 10.9.2 because:
- Safari, Chrome, Firefox are all affected on both computers in primary and guest user accounts.
- I have a 10.9.2 known-good OS (no user settings - clean install) installed on an external HDD. When I use this as a boot drive, the issue does not persist.
- I have a bootable Linux drive, same result (issue does not persist).
- Ping testing shows nothing abnormal (less than 0.0% drops) on affected units.
- Issue persists on multiple networks (one has WPA2 Enterprise, one has WPA2 Personal, the last is an open password-less network).
- Again like the OP, rebooting temporarily resolves the issue.
- Anecdotally, a colleague has the same issue on a 15" Retina, and the issue persists with a clean 10.10 Yosemite install.
Since this seems to be tied to an update, it is worth noting the 10.9.3 (http://support.apple.com/kb/HT6228) and 10.9.4 (http://support.apple.com/kb/HT1222) combo update pages shows that Safari received a 7.0.3 and 7.0.5 update during this timeframe.
To anyone with knowledge:
What OS level components could have been updated in Mavericks after 10.9.2 that would affect browser activity?
Where would you be looking for a resolution?