Hello,
None1975.
It's OK. Don't worry. I don't mind the possibly harsh language.

I'm not the kind of person who always wants the most recent software - to the contrary. One of the reasons why I left Ubuntu (LTS, even) for Debian (and like Debian so much) is exactly because I wanted, above all,
stability - and don't mind having slightly older software.
But, in this case, I really need to be able to watch videos on Real.Video, because of censorship on other mainstream alternatives.
And, I can't really choose between the lesser of two evils... Since, Real.Video will now be the place where one of my main sources of information will post its videos, and I really need to have my "Book Antiqua", "Helvetica" and other fonts rendering properly on my blog, so that I can know how well do my texts appear to my readers.
I believe that with Dai_trying's instructions I will be able to solve my problem.
Hello again,
Segfault.
In my case, my problem is really only with this particular website. Since, as I said, I can watch videos on any other video sharing website.
(And, the great improvement in speed that I observed with the new Quantum version of Firefox, is an unusual occurrence with new versions of this web browser, I believe - since, Firefox doesn't seriously alter its engine all the time.)The video sharing website in question, that I want to use, is a kind of "grassroots" initiative, that was created in response to the growing censorship on sites like YouTube. So, the people building it don't have that much financial resources, I guess, to build a good quality website that is compatible with all sorts of web browsers.
I still like Debian's conservative approach to stability very much. Since, I often use my computer for serious and important stuff (including correspondence) and really cannot afford to have instability on my computer (which I have had, with other distributions, on critical moments.)
I will then reinstall Debian still today, and hopefully post here some good news afterwards.
I just *love* the stability, much more bug-free nature, and also modular installation options, of Debian. Apart from the unfortunate adoption of "systemd" (viewtopic.php?f=20&t=129881&start=165#p671030) this distribution is *great*.