Pale Moon
Pale Moon is an independent browser, originally forked from Firefox, as a free, open source web browser with continuing development by Moonchild Productions. It is actively developed and uses many open standards. As an added benefit there is some compatibility with some Firefox add-ons along with its own unique add-ons.
This browser is available for multiple platforms including Windows, Android, and Linux. Pale Moon developed 64 bit versions before Mozilla Firefox and continues to innovate on industry standards and user input.
While there is no official ported Greasmonkey for Pale Moon there is some activity at the Greasemonkey "Fork" branch. Please read carefully this authors release notes regarding Long Term Support.