Hi, Someone is trying to visit our website but keeps getting a 520 error response. It appears that their user agent is being blocked at some point but I don't know why or where (I have tested the user agent in browser tools and get the same response). Yet, using it to visit other websites works fine, likewise if they test using another user agent they can access the site. We use Cloudflare but I don't think the issue is their end as we have sites hosted elsewhere which can be accessed through the CDN with the same user agent. Checking the server logs shows no sign of the visitor's IP address accessing the site. The user agent is: Mozilla/5.0 (Windows NT 6.1; rv:33.0) Gecko/20100101 Firefox/33.0 Just wondering if anyone can suggest how I might be able to narrow down where to find the issue or what I should be looking for? 33 seems like quite an old version, could it be the server doesn't accept visits from an older version? Many thanks