Specific URL is not opened in its default container

Multi-Account Containers Version:
Operating System + Version: macOS 10.15.2
Firefox Version: 71.0
Other installed Add-ons + Version + Enabled/Disabled-Status:
```
Extensions
----------
```

Name: Amazon.co.uk Version: 1.1 Enabled: true ID: amazon@search.mozilla.org

Name: Amazon.com Version: 1.1 Enabled: true ID: amazondotcom@search.mozilla.org

Name: Bing Version: 1.0 Enabled: true ID: bing@search.mozilla.org

Name: Dark Reader Version: 4.8.6 Enabled: true ID: addon@darkreader.org

Name: Decentraleyes Version: 2.0.13 Enabled: true ID: jid1-BoFifL9Vbdl2zQ@jetpack

Name: DuckDuckGo Version: 1.0 Enabled: true ID: ddg@search.mozilla.org

Name: eBay Version: 1.0 Enabled: true ID: ebay@search.mozilla.org

Name: Ecosia Version: 1.0 Enabled: true ID: ecosia@search.mozilla.org

Name: Enhancer for YouTube™ Version: 2.0.99 Enabled: true ID: enhancerforyoutube@maximerf.addons.mozilla.org

Name: Firefox Multi-Account Containers Version: 6.1.1 Enabled: true ID: @testpilot-containers

Name: Focus Version: 2.1 Enabled: true ID: {0a3ac859-ffdf-410c-8b9c-b328a00b5058}

Name: Ghostery – Privacy Ad Blocker Version: 8.4.5 Enabled: true ID: firefox@ghostery.com

Name: Google Version: 1.0 Enabled: true ID: google@search.mozilla.org

Name: LEO Eng-Deu Version: 1.0 Enabled: true ID: leo_ende_de@search.mozilla.org

Name: Multi-touch Zoom Version: 0.95 Enabled: true ID: {90b5a72e-cdbd-49df-8304-5b5d6ea84a0f}

Name: Twitter Version: 1.0 Enabled: true ID: twitter@search.mozilla.org

Name: uBlock Origin Version: 1.24.2 Enabled: true ID: uBlock0@raymondhill.net

Name: Wikipedia (en) Version: 1.0 Enabled: true ID: wikipedia@search.mozilla.org

Name: KeePassXC-Browser Version: 1.5.4 Enabled: false ID: keepassxc-browser@keepassxc.org

Name: Mendeley Importer WebExtension Version: 2.0.54 Enabled: false ID: @mendeleyimporter

Name: Screengrab! Version: 2.16 Enabled: false ID: {02450914-cdd9-410f-b1da-db004e18c671}

Name: Vue.js devtools Version: 5.3.3 Enabled: false ID: {5caff8cc-3d2e-4110-a88a-003cc85b3858}



### Actual behavior
Note, in the following I use this specific URL for which the issue happens on my computer (all the other URLs do work just as expected), but the issue itself is probably not related to the URL, so you may want to replace the URL with another one when testing.

Opening `https://isgroup.atlassian.net/wiki/spaces/N/pages/1366720820/Annotation+Workflow+for+WCL+Classifier+Draft` in a new and empty tab does not create a `Work` container but simply opens in the default container. Only when clicking on some link within the website, it will open a new tab associated to the container `Work`. 

Besides the issue above, when in this new tab (that should have been opened in the `Work` container but was in the default/none container) clicking on the multi-account-containers icon
<img width="29" alt="image" src="https://user-images.githubusercontent.com/18700166/71818202-98796700-3088-11ea-9762-28a5601cff43.png">
nothing will happen, i.e., the addon's menu does not become visible.

### Expected behavior
The URL should be opened in the `Work` container.

### Steps to reproduce
1. Set `isgroup.atlassian.net` to always open in container `Work`
2. Press CMD+T (or select "New Tab" from File menu)
3. Paste `https://isgroup.atlassian.net/wiki/spaces/N/pages/1366720820/Annotation+Workflow+for+WCL+Classifier+Draft` in URL bar and open it.

### Notes

mozilla / multi-account-containers

Specific URL is not opened in its default container #1609