Reuse available numbers doesn't work when temporary containers are manually deleted

[ownchoice]

• Temporary Containers Version: 1.9.2
• Firefox Version: 88.0.1 (64-bit)

Actual behavior

When I manually delete a temporary container, its number doesn't get reused and it's like is still in use, but I don't see the container, so it seems like it was indeed deleted but its number isn't being reused.

Expected behavior

The number should be reused since the containers are deleted.

Steps to reproduce

1. Create a new temporary container.
2. Close all tabs using that temporary container that was just created.
3. Go to Options > Containers (about:preferences#containers)
4. Delete that container
5. Create new temporary containers
6. The number of the manually deleted container doesn't get reused

Notes

Some time ago, I fixed this by resetting the whole browser to default values, but it's a lot of work to get everything setup again when the only thing that I wish is for the add-on to reuse the available numbers.