Thanks Tony.
Good to know that Tiddly community is working on a solution. I have been using TWC for over a decade now and I have so many plugins and customizations built in that 1. my productivity will be heavily crippled without those, 2. a large number of my scripts/customizations won't port to the modern TiddlyWiki.
I had tried multiple other solutions before I switched to TiddlyWiki. I even asked a question on slashdot for suggestions and finally, accidentally stumbled on TiddlyWiki. Though not a web programmer or a JavaScript programmer, thanks to Eric Shulman and others on this forum, I became a JavaScript programmer over the years!
When I started with TiddlyWiki, I completely missed that it depended on some obscure loophole that apparently Firefox had and has covered up now! Not sure if I would have opted for this if I had paid attention to that aspect.
I use portable Firefox on my USB drive where I keep all my TW files. But it would be often nice to be able to access them via Desktop Firefox as well - just a matter of convenience.
The latest Portable App version of Firefox is 55.0.3 (64-bit) and TWC works fine with it. It even supports most of ES6 (with Promises and other good stuff) for those heavily customizing their TWC.
But I feel reassured from your note that eventually the community will be able to bail me out of the potential catastrophe - thank you!