I had a problem with... Opera while adding a computer. Opera10 Beta for Linux is the default browser and when I click "Add This Computer" I get an error.

Thanks for reporting the bug, but can you please be more explicit about those error messages?

If you don't remember you can replicate by doing the following:
1. Run 'seahorse' application
2. Go to the last tab ('Passwords') and scroll down the list to an item called 'UbuntuOne token for https://ubuntuone.com' (or similar)
3. Right click on it and select Delete from the popup menu
4. Then try again authenticating and copy to this bug any error message that you see

The seahorse thing will just remove the OAuth token, so it will get you again through the whole process

I followed Rodrigo's instructions above and used Opera 10 Beta 1 as my default browser to try to reproduce. I was prompted for my login, then asked to "Add This Computer". After clicking "Add This Computer" I received the following error page:

"A page on the public Internet requests data from your computer. For security reasons, automatic access is blocked."

I did a search for this specific message and found several Opera forum threads noting that since Opera 9.5, the browser will block calls back to the localhost as a security precaution.

http://my.opera.com/community/forums/topic.dml?id=259892

As far as I can tell, the best workaround is to either use an Opera version prior to 9.5 or a different browser to complete the Ubuntu One setup process.

Can confirm that, see attachment.

I didn't have a problem with this.

I use Opera 10.10b as my default browser and the security warning appears, I click on Continue and the process completed successfully.

I found, however, another problem which I will report as a separate bug: "File list gets stuck on Opera (Loading...)"

Marking as Won't Fix as we will not change current versions to support Opera and other browsers that do not allow access to localhost web servers from public sites. The workaround is to set a different default browser to setup Ubuntu One and then switch back to Opera.