Will Linux GRAMPS import .fbc and .ftmb files?
If not, is there a stand alone Linux utility that will convert .fbc and .ftmb to gedcom?
As far as I understand, anything that works on one OS in GRAMPs works on all OSes. None of the usage documentation differentiates based on which OS it's running on (at least that I've seen; I'm a Mac GRAMPS user).
If it doesn't work or doesn't work properly, I'd recommend contacting MacKiev (the company that currently owns/produces Family Tree Maker) to inquire about converting to GEDCOM format without the full application, or requesting help on a GRAMPS mailing list.
I attempted to import a
*.ftmb file into Gramps 4.2.8 for Linux and it didn't recognise the format.
Consequently, it appears that Linux Gramps is unable to import