Midori useragent does not specify full operating system

Thank you for reporting this to Ubuntu. I linked a Debian report with a similar request. I don't believe we should carry a diff from Debian just for this, but if you can answer the Debian maintainer's request, then Debian might be willing to include it as well. The request is:
  If you can cite a standards document (e.g. an IEEE RFC or a W3C TR)
  that tells me to include "Debian" in the User-Agent string, I'll
  consider it.

Epiphany identified as Debian until a few months ago, and I filed a bug against that, which Canonical fixed.

As long as somebody within Canonical has been made aware of the bug, which given the long list of notified persons I think is probable, nothing else needs to be done by either you nor me. They know what they're doing.

Generally, this type of fix should be made upstream. In the case of Epiphany, we already had a diff with Debian, with Midori we don't and I don't think this is worth introducing one. In addition, for Epiphany, the change existed and was accidentally dropped. It does not seem like Midori ever had this in Ubuntu. Also, please note that Midori is community supported. We try not to create a diff with Debian unless it's necessary as this requires a developer to manually update the package. If you do not have an answer to the Debian maintainer's request, I will just close this bug as Won't Fix like the Debian one.

Browser useragents really should be generated on first run or at install time using $ cat /etc/issue

Altering a package just to fix a useragent is the wrong way to go about it entirely, but it's the way everyone has been doing it for a long, long time.

If it would please everyone, I would gladly apply $50 to the upstream development of $ cat /etc/issue - based useragent generation. I just really doubt anyone would accept that solution either. This isn't an issue I expect the community to be particularly interested in, as it pertains primarily to branding. If the community bears the full burden of maintaining the package, I don't expect them to try to fix this. Wontfix is fantastic, as long as the bug record remains accessible for maybe a few years.

Thank you for the update. Bug records should be around as long as Launchpad is, which we hope is a very long time. :) Marking Won't Fix for the time being. If Debian ends up including this in the future, I'm happy to fix it for Ubuntu as well. Please report any other issues you may find.