I use firefox (openSUSE version) with the plasma integration extension.
With this setup, when downloading a file, a notification panel shows up above the tray icons with a countdown and a progress bar. Although the countdown works properly, the progress bar stops almost immediately and remains stuck until the end of the download.
STEPS TO REPRODUCE
1. Start downloading a file with Firefox
2. Notification panel shows up above the tray icons
Progress bar stops shortly after download begins.
Operating System: openSUSE Tumbleweed 20210105
KDE Plasma Version: 5.20.4
KDE Frameworks Version: 5.77.0
Qt Version: 5.15.2
Kernel Version: 5.10.4-1-default
OS Type: 64-bit
Processors: 8 x Intel Core i7-1065G7
Memory: 15,3 GiB of RAM
Graphics Processor: Mesa Intel Iris Plus Graphics
*** This bug has been marked as a duplicate of bug 430544 ***