When you attempt to access a site that you've previously accessed through a proxy server, Zotero can automatically redirect you through your proxy.

If a site is inaccessible through Firefox when Zotero is enabled but works in other browsers or when Zotero is disabled, there may be a problem with a proxy setting that Zotero has stored.

To help ensure this doesn't happen in the future, please perform the following steps:

1. Generate a Debug ID for an attempt to load the page.
2. Open the Proxies pane of the Zotero preferences and look for a relevant proxy entry. Copy down the Hostname and Scheme, and then double-click the entry and copy down the settings from the window that pops up.

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.