PowerFox has tweaks especially for Leopard and Snow Leopard and Mac-quality of life features. You can also try Basilisk, which is the upstream version without those tweaks.
Momiji is another variant targeting Mac OS Mavericks and other targets with ESR Firefox fixes. Works pretty well!
Finally, there is work being done to revive Safari for Mavericks and work to bring Netsurf to MacOS 9.
I kinda wish there was a build for modern macOS on Apple Silicon to see how light and fast this little browser is.