Great concept and have previously had high success. Though recently my FF has been performing like crap and today finally set out to isolate it. High CPU usage even when idle one tab open to duckduckgo. Running Ubuntu 16.04 FF latest.

First part (which I fixed)
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First problem:
-> high CPU consumed by Firefox idle. Isolated down to this plugin. (plugin enabled = 20% CPU, plugin disabled = 0-1% CPU idle)

Seems I was running an older version of the backend service, which was the root cause of this issue. (sorry didn't note which chrome-gnome-shell version was running previously).

Second issue. (no fix)
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Any attempt to close firefox (File Quit, CTRL+Q, restart FF due to addon/extension change, etc.) results in a hang and crash. Firefox spins CPU for about 1 minute then crashes.

Technical Details
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$ dpkg --list | egrep "chrome-gnome-shell|firefox"
ii chrome-gnome-shell 9-0ubuntu1~ubuntu16.04.3 all GNOME Shell extensions integration for web browsers
ii firefox 53.0.3+build1-0ubuntu0.16.04.2 amd64 Safe and easy web browser from Mozilla
4.4.0-79-generic Ubuntu 16.04.2 LTS