Hi Eric,
I did run ccleaner several times but that didn't solve the problem on the DPD Site.
Hi Sergui,
I can't check anymore, since what I did today, before I noticed your reply, was following:
- Made a back-up of my Firefox and then uninstalled it
- Did a clean install, latest version
- Imported all my bookmarks from a backup I had made
- Compared the options in Firefox with IceDragon and made them the same
- Then implemented manually all the same add-ons I used on IceDragon (Firefox didn't import them automatically

)
So this resulted basically in the fact that my Firefox looked the same as IceDragon.
And DPD Pickup showed up correctly in Firefox and I could play my game.
Then I checked in IceDragon the Facebook game, which worked again

, so there much be a Facebook glitch, probably since they seem to have done some updates again (profile pictures are square now instead of round, I noticed).
But the DPD Pickup problem was still there.
Then I uninstalled IceDragon completely and did a
clean install.
Imported all bookmarks and add-ons from Firefox automatically

Checked all the settings
Problem with DPD Pickup was solved now!
Language is set to English indeed, in both browsers.
I will add Dutch and change it and see what happens, just for the fun
