Bug in interaction between uMatrix and the Snowflake webextension (torproject)

[opusforlife2]

Prerequisites

• I performed a cursory search of the issue tracker to avoid opening a duplicate issue
  • Your issue may already be reported.
  • I also searched the existing issues at https://github.com/gorhill/uMatrix/issues
• This is not a support issue or a question
  • Support issues and questions are handled at /r/uMatrix
• I tried to reproduce the issue when...
  • uMatrix is the only extension
  • uMatrix with default lists/settings
  • using a new, unmodified browser profile
• I am running the latest version of uMatrix
• I checked the documentation to understand that the issue I report is not a normal behavior
• I used the logger to rule out that the issue is caused by my ruleset

Description

Error in Snowflake debug console, caused by a line in vapi-background.js in uMatrix:

Unchecked lastError value: Error: First-Party Isolation is enabled, but the required 'firstPartyDomain' attribute was not set.

The uMatrix setting causing this error is:

Spoof HTTP referrer string of third-party requests, when set to true.

This is a bug either in Snowflake, or uMatrix. Same issue on the Snowflake bug tracker: https://trac.torproject.org/projects/tor/ticket/33405#ticket

A specific URL where the issue occurs

N/A

Steps to Reproduce

1. Have the uMatrix setting enabled.
2. Open the Snowflake debug console in Firefox.
3. The error is visible.

Ruleset

N/A

Supporting evidence

Your environment

• uMatrix version: 1.4.0
• Browser Name and version: Firefox Beta 74.0b5
• Operating System and version: Windows 7 (64-bit)

[gorhill]

What is "Snowflake"?

[gorhill]

Duplicate of #209.