This works well and is helpful altogether, BUT I'd really prefer if it were possible for it to be put on a separate bar without it having to append code to every page.
I know this isn't this extension's fault and a limitation that came with Mozilla's transition to WebExtensions..
The appended bar sadly overlaps the URL tooltips when they're shown at the bottom of the page as well (which is the default behaviour for Firefox).

Also, it's missing an option to disable the dialogue that pops up whenever a file is opened or executed directly from the bar. The dialogue counts as an actual window that is then added to the list of closed windows. We should avoid that.