Blocking JavaScript does not work in local html files (file://...) if the character encoding is not specified.

Prerequisites

[x] I performed a cursory search of the issue tracker to avoid opening a duplicate issue
- Your issue may already be reported.
- [x] I also searched the existing issues at https://github.com/gorhill/uMatrix/issues
[x] 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...
- [x] uMatrix is the only extension
- [x] uMatrix with default lists/settings
- [x] using a new, unmodified browser profile
[x] I am running the latest version of uMatrix
[x] I checked the documentation to understand that the issue I report is not a normal behavior
[x] I used the logger to rule out that the issue is caused by my ruleset

Description

Blocking JavaScript does not work in local html files (file://...) if the character encoding is not specified. This bug does not occur if the character encoding is specified.

A specific URL where the issue occurs

See Steps to Reproduce.

Steps to Reproduce

Block JavaScript in uMatrix completely. Rule: * * script block

Create the following local html file:

<!DOCTYPE html>
<html lang="en">
    <head>
        <!-- Do not specify character encoding <meta charset="UTF-8"> -->
        <title>Test</title>
    </head>
    <body>
        <h1>Is JavaScript being executed?</h1>
        <h1 id='answer'>No, it is not.</h1>
        <script>document.getElementById('answer').innerText = 'Yes, it is.'</script>
    </body>
</html>

Open the local html file in Firefox (file://pathToFile/test.html).
Reload page (F5).
Blocking does not work and JavaScript is being executed.

Ruleset

Default + * * script block

Supporting evidence

supporting_evidence

Your environment

uMatrix version: 1.4.0
Browser Name and version: Firefox 77.0.1
Operating System and version: Ubuntu 18.04 LTS

uBlockOrigin / uMatrix-issues

Blocking JavaScript does not work in local html files (file://...) if the character encoding is not specified. #267