Ok so I just found out this:
If I minimize for example Thunderbird, it doesn’t show up in the taskbar like other apps, and I can’t actually bring it back\restore\maximize because I have nowhere to click. I have to kill it and restart it again and make sure I don’t minimize it by mistake. Add-ons like TaskTray for Thunderbird doesn’t seem to do nothing.
This doesn’t happen for Chromium for example.
I tried editing the app in the K menu and check Place in systray but that causes an error.
I am not having that problem.
I did have a problem with “liferea”. When I set it to minimize to the tray, it just disappeared when I minimized. I had to force it to show (the man pages indicated how), and then turn off tray options.
There’s a task manager setting, to only show minimized tasks. Are you using that? I don’t use that, and thunderbird works fine. There’s a taskbar item for it whether minimized or not. And I can minimize by clicking that taskbar item.
If you are configured to only show minimized tasks on the taskbar, then this might be a good to reconsider that option.