In an older version of sql developer, when I expanded "tables" and clicked "open", that table view opened (with it's tabs Columns, Data, etc). Then, when I clicked a second table's "open" entry, it would another view. So I could switch quickly back and forth between more than one table view.
Now, when I click the second table's "open" entry, it replaces the existing table. So I'm only able to have one table view open at a time. What do I need to change to get this back to the old way of working?
You need to pin the 1st editor. This can be done manually by clicking the freeze view button on the object viewer toolbar or automatically by setting auto freeze on in preferences. Tools->Preferences->Database->ObjectViewer->Automatically Freeze Object Viewer Windows