@a-ron I am a bit confused.

What do you mean access websites via FTP?
Are you trying to do an outgoing FTP connection from your network, to an FTP server in the WAN?

If yes, and you are getting connection issues, try using telnet to connect to that host on port 21.

If you cant connect using telnet, go and check in your router settings : Security > ALG > FTP ALG. Make sure its enabled.

@ku4eto - thanks for the reply.

I update websites via FTP a lot and since upgrading my router, I'm now unable to connect. 

I have got around this  with some of the sites by using plain insecure FTP - non TLS and that's working for some, but some hosts don't allow this.

FTP ALG setting is on.

Tested with telnet and got this response "Could not open connection to the host, on port 990: Connect failed"
I have added forwarders for ports 21, 20, 990 & 989 and turned off firewall but still no beans. 
standard FTP on port 21 is working, but not all hosts support that anymore. Checking Filezilla forums, they suggest a firewall?

If I use my old router - it works... 

@a-ron Another thing that came to my mind:

Usually, "Connection refused" means, that the otherside has a firewall enabled on their side.

Since you have switched the routers, check if you are still being assigned the same public IP by your ISP.

It is possible, that the domains you are trying to connect to, are filtering with firewall (iptables) the source IPs.