I wish to have access to my Greasemonkey scripts across all machines I use. I already enabled the \'Enable Firefox Sync for User Scripts\' setting on G
Just to follow up: The original method presented in the question ended up working perfectly fine, after explicitly setting up the 'gm_scripts' folder as 'available offline'. I am now using this method for approximately a month, and the edited scripts are syncing quickly, without any hiccups, between two machines.
So, my initial suspicion of Greasemonkey storing some configuration data in another place proved to be false (or it is irrelevant for the purpose of syncing).
Consequently: If anyone is looking for a syncing method of their own, locally hosted userscripts (which, AFAIK, are not supported in Greasemonkey's Firefox profile syncing feature):
Important: The only scenario tested and found working in this Q/A is when the 'gm_scripts' folder only contains locally stored userscripts, and Greasemonkey's Firefox profile syncing feature is turned off. I have not tested what happens if the 'gm_scripts' folder contains both locally stored userscripts and copies of externally hosted userscripts.