I rely on the password manager in Firefox. I have two suggestions related to password generation.
First, every site seems to require special characters, but they are never in the passwords. I came across the following instructions: If the generated password does not meet the website requirements, clicking on the password field will reveal (unmask) the password so you can edit it to meet the requirements. Apparently web developers are one step ahead of you, because I just ran into one that did NOT unmask. (It also did not allow using Paste in the Confirm Password, but that isn't your problem.) My suggestion is to let users configure the generator to generate with or without special characters.
My second suggestion is to have someplace in the password manager to generate a secure password WITHOUT creating an entry with site and ID. Just let me generate one and copy it to where I need to use it. That would have allowed me to use a highly secure password at the blinkety-blankety site that caused me the problems above. Without unmasking, without copy/paste, I used a password that I could type without going crazy.