1. for security, uppercase letter is in order to protect your wallet. more info see: https://leastauthority.com/blog/audit-of-auro-wallet-extension-for-mina-foundation/
2. In fact, you still can copy, just no copy button. it's also for protect you wallet. for know user can use ctrl+A - C - V copy it. We just don't want users to copy it, because if your clipboard is listening by other software, you lose all your assets.
3. This is a limitation of Firefox, and I can understand that you're not a developer so you don't know this.