I am a little leery about posting another suggestion being that I am a total newbie here and I seem to be annoying some people. I'll try to make this one my last.
I am almost done with what I needed MP3Tag for and I don't anticipate needing it again for the foreseeable future. That should being some comfort.
If I want to change which tag columns are displayed, I tight click anywhere in the title heading row. I get a dropdown listing all of the available tag columns. I can select or deselect as I choose. The problem is that the dropdown closes after every change. If I need to make several changes, I can't do it all at once. I have to keep reopening it. I suggest that it remain open until I click an "OK" button. There should also be a "Cancel" button in case I change my mind and maybe a "Reset" button to restore the defaults.
I'd also suggest that it provide a way for me to rearrange the columns. In many other programs, I can select an entry and then use the up/down arrows on the keyboard to rearrange things.
Finally, I'd like an "auto size" option to have the screen that will automatically change the width of the columns to fit the data. And if you really want something special, allow me to set that for each column. That is, allow me to have some columns set to auto-fit and other fixed.
Ok, I'll shut up now.
This is a really good program as it is. If it weren't, I wouldn't bother trying to improve it.