AmigaOS 3.x is currently needed for inlined GIF decoding. If you are using AmigaOS 2.x, inlined GIFs will be disabled. If Commodore never releases 3.1 we will try to provide inlined image decoding for 2.x users.
In addition, Amiga Mosaic 1.2 uses the AmigaOS 3.0 pen sharing system, so that Amiga Mosaic can allocate custom pen colors on the workbench and other public screens.