Hi David - thanks for putting this add-on together!
I'm running Firefox 60.0.2 (64-bit) on Xubuntu 18.04 with firefox-sticky-containers 1.0.1. I need to find a simpler reproduction of the following bug, but for now, here's what I have.
I have two browser windows open, each with a selection of non-container tabs and container tabs; the container tabs in each window are of one type.
My first interaction with firefox-sticky-containers after install was to select a green container tab and then click a URL in the Telegram app from the PPA at http://ppa.launchpad.net/atareao/telegram/ubuntu. As expected, the URL opened in a the right window in a green container tab. Outstanding!
I next gave the other window (containing some red container tabs) focus, selected a container tab and issued CTRL-T.
The tab which opened was a non-container tab (in the browser window which had most recently had focus).
I expected CTRL-T to open a new red container tab in the current browser window.
I'm wondering if the fact that the very first thing I opened was an URL in an external app had something to do with it.