IPv6 password form submission fails

[dd23]

My setting:
I have a Brother MFC-L8650CDW printer that has a web interface, which I can reach via IPv4 and IPv6 through https. It has a self-signed certificate and thus my browser shows a warning, which I chose to permanently ignore (I don't know if this last part is relevant, though).

The web interface offers an admin login to unlock several management features.
Here's a HTML snip from the website of the login box:

 <div class="SetBox" id="SetBoxAuthRight">
 <div id="SetBoxAuthLeft">
 <form method="post" action="/general/status.html">
 <div>Login
 <input type="password" id="LogBox" name="Ba01" />
 <input type="hidden" name="loginurl" value="/general/information.html?kind=item"/>
 <input id="login" type="submit" value="&nbsp;" />
 </div></form></div></div>

My problem is the following:
Using the printer's IPv4 address, the login works fine in all cases. Using its IPv6 address, the login fails. There's no error message. The same website just reloads when I submit the password.

This happens only in Firefox 47.0 when uMatrix 0.9.3.6 is activated with default settings. Everything works fine when I manually deactivate the filter for that particular website (IPv6 address).

The problem does not occur in Chromium 51.0.2704.103 (64-bit) with uMatrix 0.9.3.3.

Let me know if you need more info.

[gorhill]

What did you try to identify the issue? Did you open the logger?

[dd23]

I can reproduce the issue when I enable uMatrix entirely for this domain. The problem disappears when I disable uMatrix for this domain.
See the following picture:

When the login does not work, I can see several entries in the log (Firefox's web console, opened with Ctrl+Shift+K) like this one:
Content Security Policy: The page's settings blocked the loading of a resource at self ("script-src 'unsafe-eval' *").
These entries are not there, when the login works.

[gorhill]

Logger? It's the fist tool to use when trying to diagnose page breakage issue.

[dd23]

Sorry, wasn't aware that there is a logger in uMatrix. But here we go: Upper half is the correctly working login, lower half fails.

Apparently scripts are blocked, even though this is not supposed to happen.
The IPv6 addresses are identical in all lines.

[gorhill]

Is the IP address of the blocked scripts exactly the same as the IP address of the document pulling these scripts?

[dd23]

Yes, I have double-checked. Blocked and non-blocked IPs are exactly the same.
I copied the logger output to a text editor and did a quick Ctrl-F for the IP and all lines were highlighted.

Also, there is no other IP shown in uMatrix. The screenshots above in post 3 show the complete matrix.

[gorhill]

Ok, I will look into this. I can't remember if this uBO issue I fixed in Firefox was also fixed for uMatrix.