Rated 5 out of 5 stars

It does what any professionally developed browser should have in the first place.. being able to [mmb] entries on dropmenu bookmark lists and have them opened in separate tabs, without the choir of having re-open the same menu.

Shame its not working on 4.0bpre10

This review is for a previous version of the add-on (1.5.6). 

re: 4.0b10(pre)

Stay-Open Menu 1.5.8rc (currently available as a prerelease version on the "all versions" page) contains the required update for compatibility with recent 4.0b10pre and the just released b10 Firefox versions. I'll upload the final version in a few days unless some bug is reported.
Glad you like it, thanks.