"Multi-Account Containers" option does not appear in the context menu on specific websites

[Softvision-MariusComan]

Notes

• On Windows the issue is reproducible 100%.
• On Mac 10.12 and Ubuntu 16.04, the issue is intermittent (3 times out of 10).
• If you switch to another tab and then come back, "Multi-Account Containers" option appears under the right click context menu for container.
• This issue is related with: https://github.com/mozilla/multi-account-containers/issues/769

[Affected versions]:

• Firefox release 55.0.3 and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a Firefox profile with the latest version of the "Multi-Account Containers: add-on (4.0.2) installed.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Open a new container from the "Multi-Account Containers" button under the toolbar.
3. Navigate to https://9gag.com/ website.
4. Right click anywhere on the website's content.
5. Observe the context menu options.

[Expected result]:

• "Multi-Account Containers" option appear under the right click context menu for container.

[Actual result]:

• "Multi-Account Containers" option does not appear under the right click context menu for container.

[Additional Notes]:

• The issue is reproducible on the following websites: 1) https://9gag.com/ 2) https://www.apple.com/ 3) https://vk.com/ 4) https://www.instagram.com/ 5) https://www.360.cn/ 6) https://www.tmall.com/ 7) https://www.alipay.com/ 8) https://www.twitch.tv/ 9) https://www.aliexpress.com/ 10) https://testpilot.firefox.com/ 11) https://soundcloud.com/ 12) https://www.wikipedia.org/ 13) https://live.com/

There may be more websites like this, but I have not found them yet.

• Attached a screen recording of the issue:

┆Issue is synchronized with this Jira Task

[jonathanKingston]

Odd I can't repro this in the signed version from our github but I can in the web extension way of building the extensions.

[clement-analogue]

The same with version 4.0.3 and Firefox 57 on Ubuntu 16.04. Just clicking on any link on the website restore the context menu option.