1st I am on Windows but I think this may still apply to you.
I wanted to get the same answer as you, One question I have for you is why you want to do it? (what is the real problem) The reason I ask is I am happy links from my TiddlyDesktop [TWC] to my other wikis opening in FireFox (my Default Browser and most others and versions) because those links are to wikis served using TiddlyServer. eg;
http://192.168.1.109:8088/Local-Instances/TiddlyWiki5.html and of course this makes them saveable etc... (Note the use of a port number in the address, and the IP address is my desktop on the LAN). But that is me.
But for you
I understand you may not want to implement TiddlyServer, but interestingly I know TiddlyDesktop uses the same underlying technology (Node.JS "runtime") and I did read there is a way to access wikis in TiddlyDesktop via the host (my desktop computer) IP Address as is the case for TiddlyServer. In this case the Wikis will open for edit in your browser if not TiddlyDesktop. your links to your other wikis can become what I call Intranet addresses, rather than file addresses. The key thing is TiddlyDesktop may host and open one or more tiddlywikis but they can be accessed via an Intranet link in your browser because TiddlyDesktop can also Server them (untested).
I have not used this IP address access feature of TiddlyDesktop yet so I am not sure how mature it is, but thought it worth telling you about.
Regards
Tony