Memory leak when opening and closing chrome windows

[Fanolian]

Firefox environment: 32bit Firefox 48 (e10s disabled) or current Nightly (e10s enabled/disabled)

Steps to reproduce:

1. Install Stylish 2.0.7 in a new profile. Restart browser.
2. Without creating/installing any styles, open one tab and only in one window. Go to about:memory.
3. Minimize memory usage a few times then measure a verbose report.
4. Search for "detached" (without quote) in about:memory. It should have no detached windows at this point.
5. Open a new window or a new private window, then close it.
6. Go back to about:memory, minimize memory usage and measure again. a top(none)/detached/window(chrome://browser/content/browser.xul)/dom/event-listeners is created.
7. Repeat step 5 and 6 a few times. More top(none)/detached/… are created and cannot be destroyed unless restarting browser.

It is not a recent regression. I think I've seen it for a very long time.

Note:
Other chrome windows may leak too, e.g. Library window(chrome://browser/content/places/places.xul)

P.S.
Traditional extensions (non-jetpack/WebExtensions) like Greasemonkey and Tree Style Tabs [1] had similar issues for a long time too but fixed eventually. They may provide hints on why Stylish leaks.

[1]: For Tree Style Tabs, search for commits around 2015-11-06 to 2015-11-10 for relevant fixes:
piroor/treestyletab@9516999...000ce6b

Thank you for your extension.

Update: add commit range for Tree Style Tabs

[Fanolian]

Bug 1296099 - consider adding new event type that is fired for tab close or browser.xul window close
This bug may provide some insights as well.