Users unable to launch the published desktop from the Mozilla Firefox. 

Getting error messages : 

Error 1 

The connection to "PA-Desktop" failed with status (Unknown client error 0) 

Error 2 

Unable to launch your application. Contact your help desk with the following information: Cannot connect to the Citrix XenApp Server. The Citrix SSL server you have selected is not accepting connections.

Solution 1

Download the x64 bit Mozilla Firefox:

• Working Firefox version - 53.067 64bit 
• Non-working Firefox version - 52.0.2 32bit

Solution 2

Recommend to test the workaround provided in private fix LC9388 - Add the following string to the SSL Cipher Suite Order GPO of VDA:

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384_P384,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384_P256,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P256,TLS_RSA_WITH_AES_256_GCM_SHA384,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_RC4_128_SHA,TLS_RSA_WITH_3DES_EDE_CBC_SHA

Citrix Documentation - Transport Layer Security (TLS)