I get not wanting to install a third party extension just for this, but it would be a simple weekend project to write one to do this yourself (and install it locally to avoid the extension store shitshow)
It couldn't be simpler - you type about:tabs into the URL bar and you get a non-html plain text listing, one URL per line, of all the tabs you have open. Maybe a line break inbetween browser windows so you can tell tabs from one window apart from tabs in another ?
Just email info@rsync.net to claim this.
Get it into mainline firefox and please take our money (see above).
I have a couple of personal extensions in the store but haven't really used it much. Just wondering what your experience is