I guessing I'm on KDE 4.13 ('rpm -qa | grep -i KDE' shows 4.11, 4.12 and 4.13 depending on the rpm, the distro is SuSE 13.1). Under 12.1 I had Firefox shown as an icon on the default panel/taskbar (whatever you call it). After upgrading I removed Firefox (don't exactly remember how) and want to add Opera but i can't find out how. I tried modifying the panel, taskbar, looking at Properties for Opera and dragging the Opera icon to the panel/taskbar. Nothing worked. If I have to edit a file that's find - just tell me which one. Thanks for your help.

I just drag the icon from kmenu to the panel, when you drag it a blank grey box will appear when a valid placement for the icon in reached. you need to make sure widgets are not locked and you can't drag it on to the taskmanager portion of the panel nor the system tray

Or just right-click on an entry in the K-menu and choose "Add to Panel".

Another possibility would be to right-click on the task manager entry when it is running and choosing "Show a launcer when not running". This would create a launcher in the task manager itself, which is hidden when you start the application, much like the launchers for your Webbrowser and Filemanager that are there by default.

A side-note: you shouldn't have had to remove the Firefox launcher, as that was a generic launcher for the default Webbrowser. If you had changed the default Webbrowser to Opera in Configure Desktop (Systemsettings)->Default Applications, it would have launched Opera instead.