If you have more than one mail window opened and you install an add-on, the installation is triggered more than one time.

Steps to reproduce:

1. Right-click on a folder in the folder pane and select Open in New Window;
2. Go to the Add-ons Manager and install an add-on (either by dropping it on the tab, or install it from the search results or from a file;
3. You get prompted to install the add-on: either click Add or Cancel;

Result:
You get prompted again (and again if you have more mail windows open).

Expected results:
Installation should be triggered only once.

Last known good: 2020-03-17
First known bad: 2020-03-18
https://hg.mozilla.org/comm-central/pushloghtml?fromchange=49d25b882f41a618fa877f6213bffb46f3df3a7b&tochange=eb262dce227553b6afb6fd567e77e273d0c6e40d
Plausible cause: Bug 1621841

Still persists in 78.2.0-pre build 1 on Linux x64. At least in that combination, I get two (!) additional prompts for each window opened in the same session, even if that window is already closed.

@darktrojan is it ok to assign this bug to you? it's probably caused by bug 1621841, which you filed and for which you created the patch...

Hmz, for me this is fixed with the introduction of 82.0a1 from august 26:
Last known bad: 2020-08-25
First known good: 2020-08-26
Haven't got a clue on what fixed it though, looks like august 25 also was 82.0a1...
https://hg.mozilla.org/comm-central/pushloghtml?fromchange=0d5c4c296e6b1b252a06eb6d54a0cd19dafd2252&tochange=a6bcebe11fbcac258a895b51cfc4c44452527967
Maybe someone else can confirm the issue is resolved?

WFM with beta

Geoff, anything left to do here?

No idea what caused this or what made it go away. :-/