I observe a problem in Tor Browser 9.0.5, based on Firefox 68.5, where special Unicode-characters are not recognized as they are in Firefox 68.5.

Here, it is the symbol U+2BC8 (⯈) which causes problems. The screen shots document the error in an authentic html-page.

If you know something, thank you for sharing. Otherwise, I will just remove those Unicode characters which are not correctly rendered.

Font whitelisting does not appear in my about:config, but anyway, if the symbol in question is not part of a font, I would not understand what whitelisting could do... So basically, there is a lack of knowledge on my side and probably not a real misbehavior of Tor Browser.

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My guess, it's a font thing - some fonts have those characters, others don't.
Tor Browser runs inside some sort of sandbox and uses a set of standard fonts that have nothing to do with those installed on your system. This is by design, to reduce fingerprinting and I suggest you do not attempt to change Tor Browser's settings to force it to use a "better" font.

The question is less “what I would do” but what visitors of a page might do to have the disturbing symbols displayed correctly. My solution is (and will probably be) to create a small image where a small, icon-like symbol is needed. Tor-Browser, at least, gives me a hint on where this may be needed.

Thank you for the information, I thought that the security issue concerns fonts which are embedded in a page not symbols which are not part of a font. But both can be mingled.