Flashblock, Adblock Plus, Password Hasher. I wouldn't venture onto the 'net without these three addons. 'Nuff said.
@Claude-Eric: I find that it's better to append the user ID to the master password rather than the site tag. If you change the site tag, PH will remember the changed version next time you visit, and it's inconvenient to be tinkering with the site tag every time.
That's also how I deal with "security" questions (which of course are the biggest security HOLE if you use a strong password): I use the same site tag, and append the last word of the question, in all lowercase, to my master password. Works great.