FF???
More like WTF, actually...
The "FF" command ("FastFonts, Copyright 1986 by Microsmiths, Inc, Non-exclusive license granted to Commodore Business Machines") accelerates rendering of the "topaz" font family (8, 9 and 11 point sizes) by adding a simpler rendering path on top of graphics.library/Text.
The original graphics.library/Text function deals with all kinds of fonts, fixed-width, variable width, etc. and features only a single all-purpose bitmap glyph extraction/rendering routine.
If you know in advance what you are dealing with, then you can write special case code for the glyph extraction/rendering and on a 7 MHz 68000 machine that change could really matter.
Commodore shipped the "FF" command with Workbench 1.3, as a standard feature. However, it turned out that on machines with an 68030 CPU or better the accelerated glyph extraction showed a curious bug.
How curious? Imagine you wanted to play a prank on a friend by installing a shell command which would perform real-time ROT13 encryption for all text that would be printed on the screen with a "topaz" family font.
While this can be somewhat entertaining for a while, it looked too much like a bug, which is why the "FF" command invocation in the S:Startup-Sequence has been commented out. it's the only way to be sure.