Opera has site preferences that include content blocking and script preferences. You don't need add-ons for these. Dragonfly is also built in, so you don't need a FireBug.
For instance, right click any web page, choose Block Content... click that annoying advertisement. Click 'Done', and you're done. There are also files available that automatically populate the content blocking with known advertisement servers.
Or right-click a page and choose site preferences, and there are options for things such as enabling/disabling of JS, etc.