Yes, this and syncing(!!!) :D (even useful on the same device: Windows <--> MacOS)

By the way, your donate button on the "About" page of Tab Outliner doesn't seem to work right now. I only get:

"PayPal cannot process this transaction because of a problem with the seller's website. Please contact the seller directly to resolve this problem."

Can you confirm that or is it only me?

Ok, just wanted to suggest an alternative/addition, which may be relatively easy to implement (and might prevent stressing the future undo function too much). Just think about it. See the second click on the trash icon as a "confirm" click.

A general undo function will be needed nevertheless and it's great that you develop it :)

Of course the undo and other functions are perhaps more crucial, so maybe focus on this later ;)

How about requiring a double click for the delete?

It's unlikely to double click by accident, just change the trash can icon to a different color or so after the first click on it to signal activation, the second click trashes the tab.

Can be performed pretty fast even if multiple items have to be trashed.