K-Meleon
In this screenshot, K-Meleon is using the Pinstripe Twin theme from K-Meleon Pro plus a custom start page.
In this screenshot, K-Meleon is using the Vista7 theme and showing a variety of XUL-based extensions.
The Klassic theme that comes with K-Meleon uses simple transparencies that work well even on React OS. This screenshot also demonstrates the "tabs on bottom" preference.
Version 74 is the last version of K-Meleon that will run on Windows 2000 or earlier.
Themes and Skins & Throbbers sections.
Older versions of K-Meleon going back version 0.1.