Cannot modify Upgrade-Insecure-Requests header.

[henrik1g]

Cannot modify the newly introduced Upgrade-Insecure-Requests header line, that is always sent by Firefox 48.0 on Ubuntu. I can change other header lines with HeaderTool just fine.

This might not be a bug in HeaderTool but maybe a "Feature" of Firefox.

I need to remove this specific line from the headers when connecting to the Web-GUI of my ISP-provided DSL-router. Poorly designed firmware on the router. I can remove it manually for a request with the FF WebDeveloper builtins.