Rated 4 out of 5 stars

Hi all! As previously indicated, downloading the "pre2" version from Jeroen's site and forcing the RDF to 5.0.* maxVersion, it still looks working ;)
EDIT: I didn't notice that even the previous comment wasn't precise:
you need to unzip the XPI file (it's only a zip file) from http://extensions.sanjer.nl/index.php?page=tb_cs_prerelease, open the only RDF file you see (it's a text file) and in the maxVersion tag substitute the 3.9.* with 5.0.*. Zip and install :)

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