URL: http://www.personal.psu.edu/adr10/hu8.html
Browser / Version: Firefox Mobile 56.0
Operating System: Android 7.0
Problem type: Something else - I'll add details below

Steps to Reproduce

1. Navigate to: http://www.personal.psu.edu/adr10/hu8.html
2. Switch to reading mode.
3. Refresh

Expected Behavior:

Font encoding works.

Actual Behavior:

Suddenly I see a lot of questionmarks. They stay when I switch to normal mode.

Edit: It also happens in the desktop version of Firefox Nightly.

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