"Hide placeholder of blocked elements" prevents images from being displayed on refresh

[Dupond]

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 -> no, since it only happens when blocking images
  • 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

First of all English is not my primary language ; I'll try to be as clear as I can. Please ask if necessary.

I have read the wiki, especially About "the page is still broken after I created all necessary rules" and Per scope switches.

My searches have shown me that there are (or have been) quite a few issues regarding images not being loaded, but a search for the "Hide placeholder of blocked elements" setting doesn't show much. And I'd like to add that this issue has nothing to do with "Per scope switches".

With Firefox (any version, haven't tested with Chrome), if "Hide placeholder of blocked elements" is checked AND all images are blocked, then any image on any page is NOT displayed when I unblock it. Forcing a refresh (including Ctrl+F5, Shift+click, etc.) of the page doesn't change anything.

As advised in the Wiki, I've checked the keylogger : it shows that the images are not blocked after the refresh. However, they are not displayed on the screen.

I've thought about a possible solution, but I don't know if it can be done (so not tested): that would be to uncheck "Hide placeholder of blocked elements" and, if one doesn't want to see the grid, hide it by a custom userChrome.css.

A specific URL where the issue occurs

Any webpage, for example https://www.falkon.org/

Steps to Reproduce

1. Add the following rule: * * * block
2. Check the "Hide placeholder of blocked elements" setting.
3. Go to any webpage.
4. Authorize images (falkon.org www.falkon.org image allow).
5. Refresh the webpage: the images are still not displayed.

Ruleset

https-strict: behind-the-scene false
matrix-off: about-scheme true
matrix-off: behind-the-scene true
matrix-off: chrome-extension-scheme true
matrix-off: chrome-scheme true
matrix-off: moz-extension-scheme true
matrix-off: opera-scheme true
matrix-off: vivaldi-scheme true
matrix-off: wyciwyg-scheme true
referrer-spoof: behind-the-scene false
* * * block

Supporting evidence

Following the above "steps to reproduce", the keylogger for the https://www.falkon.org/ webpage shows:

• allowed (written in black) :
  www.falkon.org image https://www.falkon.org/images/favicon-16x16.png
  www.falkon.org image https://www.falkon.org/images/favicon-196x196.png
  www.falkon.org image https://www.falkon.org/images/kde.svg
  www.falkon.org image https://www.falkon.org/images/screenshot.png
  www.falkon.org image https://www.falkon.org/images/about.svg
  www.falkon.org image https://www.falkon.org/images/madeByKDE.svg
  www.falkon.org image https://www.falkon.org/images/falkon.svg
  www.falkon.org CSP script-src 'unsafe-eval' blob: *, style-src blob: *
  www.falkon.org doc https://www.falkon.org/

• blocked (written in red) :
  www.falkon.org -- css https://www.falkon.org/{inline_style}
  www.falkon.org -- script https://www.falkon.org/{inline_script}
  www.falkon.org -- script https://www.falkon.org/assets/js/prettify.js
  www.falkon.org -- script https://www.falkon.org/assets/js/bootstrap.min.js
  www.falkon.org -- script https://www.falkon.org/assets/js/prettify.js
  www.falkon.org -- script https://www.falkon.org/assets/js/bootstrap.min.js
  www.falkon.org -- script https://www.falkon.org/assets/js/jquery-1.10.2.min.js
  www.falkon.org -- css https://www.falkon.org/assets/css/font-awesome.min.css
  www.falkon.org -- css https://www.falkon.org/assets/css/main.css

Your environment

• uMatrix version: 1.4.0
• Browser Name and version: Firefox 77.0.1
• Operating System and version: Arch Linux

[gwarser]

OK, I can reproduce.

[gwarser]

If I unblock -> reload (no image) -> wait 20 seconds -> reload -> image is visible.

[uBlock-user]

@gwarser related to #189 ?

[gwarser]

@uBlock-user no, hard refresh does not help.

[Dupond]

@gwarser Or even just wait 20 secs -> unblock -> refresh -> image is displayed.

The minimum amount of time to wait before refreshing does seem to be around 20 seconds...

Since according to the logger everything seems to be fine as far as uMatrix is concerned, I think it would be useful to know if this can be closed as being a Firefox bug or not.

So is there anyone using Chrome or Chromium who could test the "steps to reproduce"?

[gwarser]

Wait, stop, I was wrong! I forgot about "Hide placeholder of blocked elements", sorry. Will try again.

---

It's broken everywhere, uMatrix issue. 1.4.1b0 is also affected.

[gwarser]

Broken by gorhill/uMatrix@73c8da0

---

20 seconds: gorhill/uMatrix@73c8da0#diff-015f7477396946c0612213769f5a13bfR43-R73