Hi guys! Sorry for this delay, I was very busy at work.
So somehow I managed to install my certificate in Firefox. I guess it was a system problem as my files didn't refresh and I was unable to see my files. Then after a reboot and some gymnastics I successfully imported the certificate in FF. Big thanks to everyone, especially to Zlatko for the help. Unfortunately now there's a second problem - in the moment I click on my online bank link (which is https://...) Firefox immediately crashes. Any ideas why FF crashes?