Firefox already has Do Not Track support which allows you to opt-out of behavioral tracking, Opera released Opera 12 Snapshot with Do Not Track support, which is disabled by default. You can enable this option from its Security section in Preferences from being tracked on the web.
Opera Now Supports Do Not Track
Enabling Do Not Track in Opera
1. Press Ctrl + F12 to open preferences,
2. Select Advanced Tab>Security check for “Ask websites not to track me”, click Ok to apply the changes.
Why DNT not enabled by Default?
Do Not Track is the option needed to be enabled by user as it his/her choice to opt-out from tracking, Mozilla already confirmed in the past they won’t force the users to use this feature or they’ve none plans to enable it by default, so it’s not a surprise that Opera also follows the Mozilla approach.
Currently only few sites support DNT.
You can download Opera with DNT from following links.