What is the reason for the partial availability of sites?

Question

Computer networks

Good afternoon everyone.
I'm trying to set up PPPoE on Juniper SRX100
Everything seems to be fine, but some sites are not available from the browser. For example toster.ru speedtest.net
I think that the matter is in mtu, I called and clarified which mtu, but still I can’t pick it up.
Maybe I missed somewhere in the config?
Config:

interfaces {
    fe-0/0/0 {
        unit 0 {                        
            encapsulation ppp-over-ether;
        }                               
    }                                   
    fe-0/0/3 {                          
        unit 0 {                        
            family inet {               
                address 192.168.3.1/24; 
            }                           
        }                               
    }                                   
    pp0 {                               
        unit 0 {                        
            ppp-options {               
                pap {                   
                    local-name ########;
                    local-password "#########"; ## SECRET-DATA
                    passive;            
                }                       
            }                           
            pppoe-options {             
                underlying-interface fe-0/0/0.0;
                idle-timeout 0;         
                auto-reconnect 10;      
                client;                 
            }                           
            family inet {               
                mtu 1450;               
                negotiate-address;      
            }                           
        }                               
    }                                   
}                                       
routing-options {                       
    static {                            
        route 0.0.0.0/0 next-hop pp0.0; 
    }                                   
}                              
security {                              
    nat {                               
        source {                        
            rule-set trust-to-untrust { 
                from zone trust;        
                to zone untrust;        
                rule source-nat-rule {  
                    match {             
                        source-address 0.0.0.0/0;
                    }                   
                    then {              
                        source-nat {    
                            interface;  
                        }               
                    }                   
                }                       
            }                           
        }                               
    }                                   
    policies {                          
        default-policy {                
            permit-all;                 
        }                               
    }                                   
   zones {
        security-zone trust {
            host-inbound-traffic {
                system-services {
                    all;
                }
                protocols {             
                    all;
                }
            }
            interfaces {
                fe-0/0/3.0;
            }
        }
        security-zone untrust {
            host-inbound-traffic {
                system-services {
                    all;
                }
                protocols {
                    all;
                }
            }
            interfaces {
                pp0.0;
            }
        }
    }
}

concerning

policies {
default-policy {
permit-all;
}

for test purposes sake =)
Thank you.

Answer 1

The problem is either with certificates or with MTU.
1. Cardinally. Reduce MTU to 1000 tcp mss to 960, if it helps, then raise it to max. value at which everything works.
2. If only https sites do not open, look at the system time, certificates, etc.