Helpful. Well done. And, please...? Rated 4 out of 5 stars

Feature request: automatically, silently import cookie txt file backups on browser launch.

Extra please with sugar and so forth. :)

This review is for a previous version of the add-on (1.5.1). 

That is something this extension never meant to do and probably never will, sorry.
However, a restartless extensions just for that purpose could be done in 10 minutes ;)

[UPDATE]
Here is restartless, 2kb, 30minutes worth of coding addon:
https://addons.mozilla.org/en-US/firefox/addon/auto-restore-cookies-on-startu