Hi!
I noticed, that in Xymon 4.3.30 opening the "Snapshot Report" (snapshot.sh) as well as the "Availability Report" (report.sh) in the "Reports" menu do not work as expected, but try to download a file snapshot.sh or report.sh.
Digging deeper into this, I noticed, that this seems a Firefox only problem, while chromium works without problems.
In the code web/snapshot.c and web/report.c I found a variable usemultipart, which is 1 by default and is reset to 0 if HTTP_USER_AGENT contains "KHTML", which (according to a comment) cannot handle multipart documents.
It seems, that current Firefox also can not handle this correct, while Chromium uses the User-Agent "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36" so it already disables multipart.