Make sure you are not blocking content.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Thanks for the idea. I never knew you could start Firefox in safe mode.

Unfortunately the problem persist, though.

Is there anything else I can try?

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Ah, found this back again! Lost the link. Sorry for the late reply! I'll try your solution and see if it works.

BTW, I just thought to try out the website in Chrome and Edge. In Chrome the video didn't load either without any message.

In Edge it didn't load and said: "Error: Source not supported"

Could this be the case in Firefox/Chrome as well, while that error message isn't displayed? If so, how can I make it happen that the source is supported?

ETA: I've also checked this, but unfortunately I don't see an option to activate the flash plugin. I've tested the flash player and Adobe's site says : "Congratulations, your computer has the latest Flash Player installed. " So it seems it should be working......

Oh, and ABP is disabled on this site, as well as Firefox own block.

ETA2: Okay, I've also tried this:

Try switching these settings, since Firefox on XP can't handle these formats anyway:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste mp4 and pause while the list is filtered

(3) Double-click the media.mediasource.mp4.enabled preference to switch the value from true to false

(4) Double-click the media.mp4.enabled preference to switch the value from true to false

Then do a reload of the page bypassing the cache (Ctrl+Shift+r). Does that help the site's player over to Flash?

Unfortunately all that gives me extra is: Error: no Valid source could be found.

Oh, I noticed I forgot to tell you that I have Firefox 58.0.2 installed. Don't know if that makes a difference....

ETA3: I've also checked for these: This involves modifying some preferences on the about:config page. media.gmp-eme-adobe.enabled (boolean, true) media.gmp-eme-adobe.forceSupported (boolean, true; FF 49.0+) media.gmp-eme-adobe.visible (boolean, true; FF 49.0+) media.gmp.decoder.enabled (boolean, true) media.eme.enabled (boolean, true)

But none of these are in my Firefox version. The only ones I see are: media.gmp-eme-adobe.abi (string, x86-msvc-x64) media.gmp-eme-adobe.lastUpdate (integer, 1476111993) media.gmp-eme-adobe.version (string, 17)

Unblocking dangerous and intrusive Flash content didn't work either.

ETA4: Well, I've just restarted my computer in safe mode, tried to view the video on the website again and unfortunately it still doesn't work.

Additionally, I've also tried it in Commodo IceDragon (cause I saw that somewhere else as a suggestion), but that didn't help either :(

ETA5: BTW, I had pout the following to true again: (3) Double-click the media.mediasource.mp4.enabled preference to switch the value from true to false

(4) Double-click the media.mp4.enabled preference to switch the value from true to false

Otherwise videos on Facebook and Twitter wouldn't play anymore.

Go to the top of any support.mozilla.org web page and press your user icon to see your Mozilla profile. Including your questions and answers.

If three different browsers have the same problem, then it is likely a website issue. Contact its support.

I'll be damned! Thanks :) Now I look where to look for in the future when I've posted a question :D

I've contacted support indeed today. Keeping my fingers crossed they'll respond :)

I'll keep it open for now, hoping I'll get the solution from either the website owner or Adobe (you never know)....

When I get an answer, I'll post it here for others with the same problem to find.

Well, as it turns out it actually is the problem that I don't live in the USA. Too bad. :(

If you want, find a proxy you can use.

Thanks! I've found a solution :)