[webextension] "Block element" does not appear in menu for some websites

[mapx]

Environment

Firefox 57
ABP 2.99.0.1896
easylist / easyprivacy

ALSO

Firefox 60.0.1 / 64.0
Adblock Plus devenv built from ​96eda29ae585.
Default filter lists

How to reproduce

1.) Browse to ​https://www.bestbuy.com/?intl=nosplash OR ​https://facebook.com OR ​https://tweakers.net/ OR ​https://www.dpreview.com/ OR ​https://vk.com/
2.) Click the ABP icon

Observed behaviour

"Block element" button is missing.

Expected behaviour

"Block element" button is shown and functions correctly.

Notes

• ​An error shows up in the background console when the popup is opened, but only when the problem is happening:

Unchecked lastError value: Error: ext is not defined  ExtensionCommon.jsm:304
	withLastError resource://gre/modules/ExtensionCommon.jsm:304:9
	wrapPromise/< resource://gre/modules/ExtensionCommon.jsm:357:11

• This does not seem to be a recent regression, I tested quite far back and could consistently reproduce the problem.
• I can still reproduce the problem with EasyList disabled.
• This seems to be a symptom of ​Mozilla bug #1408996.
• See ​this workaround in uBlock: var vAPI = window.vAPI;.

Hints for testers

• Check that the "Block element" tool works for these troublesome pages on Firefox now.
• Check that subscription links still work on Firefox.
• Check that the "Block element" tool works as before on Chrome.

[kzar]

I can reproduce this as described, investigating.

[mapx]

Could be related to this ticket ?
https://issues.adblockplus.org/ticket/5817

Does FB use some restrictive CSP directives ?

[kzar]

Replying to mapx:

Could be related to this ticket ?
https://issues.adblockplus.org/ticket/5817

Does FB use some restrictive CSP directives ?

Well since the error is showing up in the background page I figure it's not likely to be the problem, but for reference the CSP I'm seeing is default-src * data: blob:;script-src *.facebook.com *.fbcdn.net *.facebook.net *.google-analytics.com *.virtualearth.net *.google.com 127.0.0.1:* *.spotilocal.com:* 'unsafe-inline' 'unsafe-eval' fbstatic-a.akamaihd.net fbcdn-static-b-a.akamaihd.net *.atlassolutions.com blob: data: 'self';style-src data: blob: 'unsafe-inline' *;connect-src *.facebook.com *.fbcdn.net *.facebook.net *.spotilocal.com:* *.akamaihd.net wss://*.facebook.com:* https://fb.scanandcleanlocal.com:* *.atlassolutions.com attachment.fbsbx.com ws://localhost:* blob: *.cdninstagram.com 'self';

[kzar]

I'm not sure what's going on here, popup.js is sending "composer.content.getState" but getting undefined as the response. I've ran out of time for today.

[mjethani]

Well, I've narrowed it down. The problem here is that ext in ext/content.js is undefined. But that's only the symptom of the real problem, which is a bug in Firefox.

You can try out the simple extension below.

Here's the manifest.json:

{
  "applications": {
    "gecko": {
      "id": "example-extension@example.com",
      "strict_min_version": "50.0"
    }
  },
  "content_scripts": [
    {
      "js": ["content.js"],
      "matches": [ "http://*/*", "https://*/*" ],
      "run_at": "document_start"
    }
  ],
  "description": "An example extension",
  "manifest_version": 2,
  "name": "Example",
  "short_name": "Example",
  "version": "0.1.0"
}

And here's the content.js:

{
  const instanceId = Math.floor(Math.random() * 10000);

  console.log("Initializing content.js");
    
  let printFoo = () => console.log(`[${instanceId}] window.foo:`, window.foo);
      
  window.foo = {};
  printFoo();
  
  setInterval(printFoo, 1000);
      
  console.log("Finished initializing content.js");
}

Now when you load ​https://www.facebook.com/thebestposts you'll see that even though window.foo is assigned and prints the correct value immediately, on the first tick (after a second) it prints undefined and keeps printing undefined forever. It's like the window object is getting replaced at some point.

Interestingly this does not happen on ​https://manishjethani.com/

I'll investigate further tomorrow but this looks like a bug.

[mjethani]

I have reported the bug to Mozilla: ​#1412115.

[kzar]

​https://bugzilla.mozilla.org/show_bug.cgi?id=1408996

[mapx]

another site which breaks the "block element" feature
​http://www.eweek.com/security/north-korea-getting-ready-wage-a-global-cyber-war-experts-say

[Janevski]

Scenario:
This happens on Chromium too.
Just by visiting some websites the right click block element option doesn't appear to exist at all.

Example, but not limited to:
Visit ​http://time.mk
I've put an attachment of index.html.

Info:
Chromium Version 63.0.3239.84 (Official Build) Built on Ubuntu , running on Ubuntu 16.04 (64-bit)
Adblock Plus 1.13.5

[kzar]

Janevski that is a different issue, see #6048.

Edit: In fact that issue isn't quite the same either, I've opened #6387 for it. To set expectations however fixing this might well not be possible with the APIs that the browsers provide.

[mapx]

https://issues.adblockplus.org/ticket/6678

[greiner]

In case it helps: We've been experiencing the same issue in the Flattr extension on Firefox Mobile where the browser "forgets" ​the extension's listener which it sets on flattr.com for the purpose of authenticating the user. Unlike here, however, we didn't encounter the problem on Firefox Desktop or on Chrome.

Unfortunately, all I found about it at that time was ​bug 1408996 which has already been mentioned in a previous comment.

[mapx]

another example

https://tweakers.net/

[mapx]

No such issue in uBo, it works on every site

[mapx]

https://issues.adblockplus.org/ticket/6714

[kzar]

Replying to mapx:

No such issue in uBo, it works on every site

Seems you're right, which led me to ​this workaround in his code.

[greiner]

See also #7159

[mapx]

https://issues.adblockplus.org/ticket/7165

[abpbot]

A commit referencing this issue has landed:
​Issue 5938 - Work around Firefox content script bug

[Ross]

Fixed. Block element now works as expected on the sites listed. There is still some odd behaviour on the Bestbuy website which I opened as #7298.

ABP 3.4.3.2253
Firefox 65.0.1 / 51 / Windows 10
Firefox Mobile 65.0.1 / Android 7.1.1
Chrome 72.0.3626.109 / 49.0.2623.75 / Windows 10
Opera 58.0.3135.65 / 36.0.2130.80 / Windows 10
Edge 44.17763.1.0 / Windows 10