@phaidros I was thinking a little bit deeper about this issue. Like I said, this issue didn't appear before with the activated addon "Canvas Blocker". This addon makes sense, because it blocks Canvas-Fingerprinting.
It's important to me that I'm save on internet without any chance with tracking by software.
My question is, did Windy changed something to read out Browser-fingerprinting?
If so, please fix.

@phaidros Looks like I found out. I have deactivated the addon "Canvas Blocker". Now Windy works as it should. But strange thing somehow ... Windy worked before with the activated addon. I can't remember I have changed anything.

Anyway .... thanks a lot dear Ondrej. Very good teamwork!

@Ondřej-Šutera We are coming closer. In a private window no issue. I'm thinking about my several addons I've installed on Firefox. But they were all installed before, without issue on windy. This issue first came up maybe a week ago or so.

@Ondřej-Šutera I already did. With the Brave Browser this failure doesn't occur.

@Ondřej-Šutera I'm using the newest version of Firefox, on Linux Mint and Windows 10. On both the same issue. No problem on my Android App.