When you attempt to access a site that you've previously accessed through a proxy server, the Zotero Connector can automatically redirect you through your proxy.
If a site is inaccessible through your browser when the Zotero Connector is enabled but works in other browsers or when the Connector is disabled, there may be a problem with a proxy setting that the Connector has stored.
To help ensure this doesn't happen in the future, please perform the following steps:
Post the Debug ID and proxy details to a new forum thread so that developers can investigate.
You can then delete the proxy entry from the Proxies pane, which should fix the problem temporarily.