For easy typing of Pāli in Opera you can modify the keyboard to add shortcuts to suit your personal needs.
Spell-checking of Pāli text in edit boxes is currently only available by using a free third-party utility to copy the text to Open Office, check it there, and paste it back in when done. The spell-checker used by Opera — Aspell — is capable of checking Unicode text, but this hasn't yet been properly implemented as far as I know.
If you see square boxes below, then you either need to install a Unicode font, or change your browser to Opera or Firefox.
ḥṛṝṣś ḤṚṜṢŚ (Sanskrit)