Opera

It is not possible to recover the password for certificates in Tools > Preferences > Advanced > Security (Mac: Opera > Preferences > Advanced > Security) if you have forgotten or lost it.

The only solution is to go to your Opera profile folder (see Help > About Opera) and remove the file named "opcert6.dat", which will remove your password.

Note that this also removes your public keys and certificates. Make sure you make a backup of the file in order to keep it safe for the future, in case you happen to remember what the password was.