“Invalid tab ID” error is constantly thrown if switching back to the tab from which the screenshot was performed

[emilghittasv]

[Affected versions]:
Firefox 54.0b7 (Build Id:20170511130324)
Firefox Screenshots 6.6.0

[Affected platforms]:
Windows 10 64 bit
MacOS 10.11.6
Ubuntu 16.04 64bit

[Steps to reproduce]:

1. Open Firefox with a clean profile.
2. Enable Firefox Screenshots.
3. Access the https://www.reddit.com/ webpage.
4. Click the Firefox Screenshots button.
5. Click the “Save full page” button.
6. Quickly close the newly opened tab and open the reddit tab.

[Expected result]:
No error is displayed.

[Actual result]:
“Whoa! Firefox Screenshots went haywire” with “ReferenceError: Invalid tab ID” is constantly thrown.

[Additional notes]
Please note that ID constantly changes.
Please observe the following video for more information: https://goo.gl/sIG0NA