Actually, between all these non-free systems you used so far, I
recommend that you make Trisquel's GRUB the default.
To do so, boot Trisquel, and do:
df --output="source,target"
This'll give you a list, and when using Trisquel, the "/" mount-point
("Mounted as") must be something like "/dev/sd[Some letter, without
these braces][Some number here, without these braces]". Now, remove the
number from the file name, because what matter for us is "/dev/sd[Any
letter]".
Now do:
sudo grub-install "[The file name, without the numbers, and without
these braces]"
And finally, do (just to make sure everything is updated):
sudo update-grub
