Rated 4 out of 5 stars
I have contacts in Gmail. I want them in TB - not synced, just a copy across from my contacts in Gmail, (which is copied every once in a while on my Android phone from my work (Exchange) because work is where I need to keep and maintain my contacts. My head hurts just typing about it.
Finally a Thunderbird extension that copies *all* items, and they're all readable. Some issues with addresses not coming across, but after so long of manual exports/imports, and extensions that only copy half of my contacts, I can definitely live with it (and it's quite possibly something that I'm doing :)