I am not sure how liking works exactly, but is the browser doesn't use persistent connections it could increase the sensitivity. Having multiple browsers (or even the same browser with another window in incognito) can also create more connections. When you tried chrome, did you shut down firefox? If not, then it would only add to the simultaneous connections if firefox was causing an issue.
I just added a rule to whitelist active logged in IPs for 25 minutes. Let me know if that helps. It will not help anonymous users...and I may have to remove that whitelist or maybe have a different limit, but any bad activity can be tracked back to a user...