Hi,
I've had issues with connecting to UM with Firefox for a while due to the error "SSL_ERROR_WEAK_SERVER_EPHEMERAL_DH_KEY". IE has worked fine, but seems like MS fixed this in WIndows 10 (or one of the latest patches for IE), so now IE won't work either.
Found a KB article that helps out with this problem:
It is for the Web Client, but the common denominator here is Tomcat.
For UM, this is the file you want to edit:
/usr/local/tcserver/vfabric-tc-server-standard/um/conf/server.xml
Find the <Connector port="8443"... part of the config, delete everything from the ciphers value and make sure it is set to this afterwards:
ciphers="TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_CBC_SHA"
I would recommend doing this via SSH, but it can be done from the console as well. This is how it looks like when it is finished:
After editing, make sure to restart tomcat (I did this with "/etc/init.d/tomcat restart", you may do it differently 
)
Hope this helps some of you!