Content scripts are not loaded in Firefox on some web pages

Add-ons Development
1

I develop an extension in Firefox 76.0.1 and add a content script via content_scripts in the manifest.js. I figured out that on some pages the script is not inserted into the page. For instance, Address bar autocomplete suggestions in Firefox | Firefox Help
Here, no script is loaded at all.
Usually, it looks like this:

Screenshot_20200525_174308
Screenshot_20200525_174308434×234 12 KB

But on the mentioned pages it looks like this in the debugging tool:
Screenshot_20200525_174503
Screenshot_20200525_174503434×234 10.8 KB

I found this issue:
Stackoverflow: Firefox content script not loading in some pages, where the problem was a Content-Security-Policy in the header of the page.
But I don’t have such policy in my headers.

Does anybody has an idea what is wrong here?

2

Are you asserting if the content script is injected solely on the fact if the debugger displays it? I remember a recent post somewhere mentioning that a bug was fixed where not all content scripts were shown reliably in the debugger.

3

Some Mozilla sites are restricted, similar to some built-in pages, and you cannot inject content scripts into them. If you are using the about:debugging page => Inspect => Console, you may see a specific reference to lacking the host permission to inject into the page. (I don’t know where else it would appear.)

SUMO is in extensions.webextensions.restrictedDomains which is user-editable, unlike the built-in pages issue.

1 Like
4

No, I first saw that the script did not answer.
Thanks for that remark.

1 Like
5

Indeed, in this case it was the restricted domains :slight_smile:
Thank you very much.