Cross-Platform (Windows 32, All UNIXes, Mac OS (Classic and X))
The most complete browser todate in its support for standards.
(some things are still missing, but work is carried forth in this
direction)
Has many registered bugs, but
they are relatively rarely encountered. (better than most other browsers, at
least)
Still relatively under-used in comparison to MSIE. (at least on
Windows, which is the most common platform)
Its developers made a conscious decision, not to support the
MSIE deviations and extensions from the W3C standards, and so it often
breaks in sites that only work in MSIE.
Verdict
Make sure your site supports this browser.
It is available on your development platform of choice, and many people
use it.