*** IMPORTANT NOTICE ***
The online viewer option will be removed starting in version 2.2. If you use this feature and still want to use it afterward, please install "Swiss Knife", a new extension for Opera. Do not worry, you can port your settings to the new extension using the backup/restore feature on the preference page.
This extension automatically redirects you to the secure version of web pages. It also modifies the links on pages you open to make them point directly to the HTTPS version (those rules can be edited from the preference page).
* Google (Gmail, Reader, Calendar, Picasa, YouTube, etc.)
* New York Times
* The Pirate Bay
* Many others
To add your own rule, click "Menu" > "Extensions" > "Manage extensions", then click on the gear beside "Redirect to HTTPS" and click "Preferences".
KNOWN ISSUE: The insecure page is still loaded for a few milliseconds, meaning some of your information might still be exposed. Unfortunately there is no way to solve this with the current extension API.
PLEASE REFER TO THE 'HELP' SECTION ON THE EXTENSION'S PREFERENCES PAGE TO REPORT BUGS