[CentOS] Greasemonkey question

Hello all,

Sorry about going a bit off-topic (the question is not really
Linux-related) but here it goes nonetheless:

1) How does one create a webpage with a Greasemonkey script that is installable?

2) Why does it happen that a Firefox installation in a user's account
(i.e., the configuration which amongst other things contains
Greasemonkey scripts) would all of a sudden lose them?

Thanks.

Boris.