NCSA Mosaic for Microsoft Windows User's Guide
Occasionally, you may want to abort the retrieval of large documents
or documents stored on distant servers which require greater transfer
time. At any point in a data transfer process, you can click on the
spinning NCSA Mosaic icon in the upper right corner of the window to
stop the current network action.
The NCSA Mosaic icon appears to the right 
of the Title/URL bar
Most WinSocks for Microsoft Windows Version 3.1 support an interrupt.
However, the WinSock in Microsoft Windows NT does not support an interrupt,
so NCSA Mosaic file transfers on a Windows NT platform are not interruptible.
National Center for Supercomputing Applications / mosaic-win@ncsa.uiuc.edu