Do you have Kapsersky antivirus?

Firefox 44 and newer accepts a new kind of encoding (compression) called Brotli (br) for secure connections and Facebook turned on Brotli encoding back in May. Firefox 44.0 and newer works fine with this change.

If you do have Kapsersky and do not have its definitions updated then it may be affecting this br encoding and strips it from the HTTP response headers if you have "Inject script" checked in Kapsersky Settings -> Additional -> Network -> Traffic Processing

See also https://forum.kaspersky.com/index.php?showtopic=351027 on the history of this.

It has been fixed in Kapsersky since oh May 13.

Thanks for responding, James. Nevertheless, I do not have Kaspersky on my computer... Therefore, I still don't know how to fix this issue...

Well your description of issue sounds like above example. If Firefox 43.0 is able to work then perhaps some application like a antivirus or scanner or such that can deal with your connection is affecting the Brotli encoding on Facebook like the Kapsersky antivirus did for Firefox 44.0 and newer users.