matthijskooijman/firefox-gnome-keyring — comment on commit 05ca88ac3e3a580f3a0a216dc8c1f8297767c510
File:  line 0
By fat-lobyte:

There is code that detects the maxVersion automatically by looking at the version of the installed xulrunner executable.
Try if this works for you:
https://github.com/infinity0/firefox-gnome-keyring
If not, you could try with "make VERSION=8.0".