I offer an alternative to above.
Firstly I have not yet submitted my new fav cursor. I may change my mind?
But thanks to this post by Rich, I too saw a change in my cursor. Beauty is in the eye of the beholder.
quick fix without yet making a TCE
1) download a icon theme that you like from
https://www.gnome-look.org/browse/cat/107/order/latest/Alho link is latest.....you can choose latest rating or plinged
2) unpack the download and ensure it contains a *theme
3) use root powers to move unpack to /usr/local/share/icons
While there observe the other names of cursor themes there YMMV
eg Adwaita hicolor redglass whiteglass
You will need to know that syntax to adjust the gtk3 config file
so mine is now
gtk-cursor-theme-name = oxy-neon
4) exit and restart FF to see what a diff your preferred cursor theme is.
I won't show the insert bar icon as most people should know its just a I...but if interested
the grab bar inside FF to grab or action a link changes to
https://imgur.com/nMC4HYCWhile the pointer for clicking (say) the bookmarks in FF looks like
https://imgur.com/pWDJHce5) if you do not make your own TCE or no TCE is supplied then add that dir to your backup
/usr/local/share/icons/something
Slightly off topic
gtk2 theme for cursor and also be changed ....file is at ~/.gtkrc-2.0
You will need to open a gtk2 app to see the diff.
Hope that helps someone
EDIT
or place icons under your home ~/.icons...not yet tested too busy