Updated Rated 5 out of 5 stars
I have 8 gigs of RAM and an i-5 230ghz processor, running Windows 7 Home with all updates current, and Avast firewall.With just a few tabs open, or even 1, it takes anywhere from 5-15 seconds for Firefox to close a tab, and about 2-6 seconds for it to open a new one. I disabled all add-ons, and re-enabled them one at a time. This add-on was the culprit. With it disabled Firefox is fast again.This is not intended as a bug report, but a review to let others know in case they experience a similar problem.
I received an email from the developer with a link to the updated version. Problem resolved. Very happy to have this extension back.
New version in beta - pending approval
More info here: https://www.evernote.com/shard/s13/sh/a85447d9-3dae-44ac-8380-2aaa1a00840c/1f0f0afa513b35744903b1ba47ac29cf