How do inject a script into a website *before* the first script on this website is able to run?

[The 8472]

On 15.08.2017 18:00, Manuel Reimer wrote:
> It actually works if I place my whole code directly inside my content-script.

You really should not load things via a <script> tag when you actually want to run it as content-script. Those are separate security scopes.[0]
If you just want to load some library into the content script context before your page script loads specify both in the manifest, it takes an array[1]



[0] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Content_scripts#Content_script_environment
[1] https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/content_scripts#js