Hi Konstantin,
Thanks for your reply, 

> What Linux? (on most linuxes, run "lsb_release -a")
> What version of midas? (run odbedit "ver" command)
I am using CentOS 8

> What version of firefox? (from the "about firefox" menu)
Firefox 71.0

Thanks 
Mehran

> No you cannot fix it from inside firefox. The issue is that the overlap of encryption methods
> supported by your firefox and by your openssl library (used by mhttpd) is an empty set.
> No common language, so to say, communication is impossible.
> 
> So either you have a very old openssl but very new firefox, or a very new openssl but very old 
> firefox. Both very old or both very new can talk to each other, difficulties start with greater  
> difference in age, as new (better) encryption methods are added and old (no-longer-secure) 
> methods are banished.
> 
> BTW, for good security we recommend using apache httpd as the https proxy (instead of built-in 
> https support in mhttpd). (I am not sure what it says in the current documentation). (But apache 
> httpd will use the same openssl library, so this may not solve your problem. Let's see what 
> versions of software you are using, per questions above, first).
> 
> K.O.