EDIT- It appears that there is a working 4.0 Rated 5 out of 5 stars
It appears that they did get the new version out but it is listed as experimental so far. It doesn't show when I did searches for it but it can be found. If you scroll down to the bottom of the "ME" page and look for "list all versions" the 1.0b1 version is the one working for 4.0
EDIT2 ** A few months later I am attempting to install it for TB 3.11 but it failed there. It would have been nice to be able to install collections on TB
Experimental beta for Firefox 4 now available
You can get the download by clicking "View all versions" at the bottom of the listing page (look for the version 1.0b1). Please read release notes before downloading and don't forget to report any bugs on the support forum.