Extra Folder Columns

Z 4 z 5 gwězdkow pógódnośony

wót Barleyman74 dnja Dec. 6, 2009 · trajny wótkaz

It's easy enough to patch to work for release candidates. Open the xpi file with 7zip (or winzip or whatever) and change the line 14 to say
3.1

which should make it work for now. Same as psik0tik's advice except won't expire with next release candidate.

There are some issues with the add-on like the folder size doesn't seem to be accurate.