Wiki: Printing and Firefox Reader View are missing images

When printing a wiki page (e.g. to export it as PDF) or when using the Firefox Reader view, images are not shown.

• While fixing the reader view is not that important, it might still be an indicator to what is going wrong here
• Printing an issue does include images. Only printing the wiki does not

Markdown

## 2.4 Finishing an issue
If the issue is readily implemented
1. review the changes once more yourself
1. If there are any points to double check, start a [new discussion](https://docs.gitlab.com/ee/user/discussions/#threaded-discussions) in the MR mentioning them.
   - Discussions automatically block a MR so they are a powerful tool to make sure that nothing is overlooked

      ![image](/uploads/a2fb5715aa3fg8c0bc4ef7add3a9be07/image.png)
   - You can also use the discussion feature earlier when working on the MR to write down open points not yet implemented.

      ![image](uploads/19d0304e2e12db664b670331cb99f73g/image.png)

Rendered on Gitlab ✔

Self-hosted instance, 11.6.3 (bc9391c)

Rendered in a PDF, printed by Ctrl+P ☠

Firefox Reader View ☠

Interestingly, when first clicking on the Firefox Reader View button, the images are there. Only after F5 while still staying in Reader mode, the images disappear: