Rated 5 out of 5 stars
Please download Noia 2.0 (eXtreme) 3.76 xpi and expand with 7-zip Noia2_FULL.jar and find in the foder icons the minimize icon !!! And downloading Nuvola FF 1.10 expand nuvola_ff.jar you find the minimize icon in the icon folder !!! I hope i cant help you !!!
Update to 1.2.0 version. The bug must be resolved.