One large content filtering provider has mis-classified our website. We reached out to them to correct this. That is likely why you may have trouble accessing our site from an organization that employs content filtering. Hopefully they'll fix this shortly...

Edited to add:

They've approved the change for our site, so at least for that content filtering software, we should be accessible once again. If the library would share what service or software they use with you, I can make sure we're clean with that service as well. (The service that just fixed its listing of us is called Palo Alto Networks.)