Actually every addon indicates on the addon site whether it is compatible with quantum or not. In some cases, there are indeed addons that are only compatible with 57+ (also indicated there), but the ones I described were accurate; I'm already using the updated versions, but they are seriously hamstrung. I agree that things are likely to slowly improve as the WebExtension APIs are extended and addons go through more updates. Still very difficult to lose so much functionality overnight. I may switch to v52 (ESR) for now, then decide next year whether to stick with Firefox.