Thanks! That does look like a good solution for moving a tab to a specific window. Serious bummer that it Sidebery doesn't include a Window selector. It appears to want to use panels, but panels can't be named. Turning off the horizontal tab bar in FF is also a hack rather than a simple setting.

(edit) UG. The only way to create a new tab with Sidebery is to use a keyboard shortcut - this makes using Multi Account Containers a serious PITA as you can't just open a tab directly into a container. so frustrating!