For a while now the transition away from Manifest V2 (MV2) to MV3 has been on-going and it looks like it is entering its final phase of deprecation, at least, in the case of Google Chrome. A recent discussion thread in the w3c WebExtensions Community Group GitHub repo has highlighted how the latest and upcoming versions of the most popular browser are expected to be its final releases with support for MV2 extensions.
What this essentially means is that the tricks and bypasses that were used to keep MV2 extensions like uBlock Origin and others alive will not work any more on Chrome, or at least not for very long. For example the Windows Registry mod that could extend MV2 availability will cease to function after Chromium version 151.
The MV3 support in firefox is even stricter than in Chrome. I found that chrome will let you sidestep CSP to make an HTTP request. Firefox won’t.
I don’t understand what you found, but firefox still supports the web request blocking API for Mv3 extensions, which is what ublock needs.
I was debugging one of my favourite extensions this week to figure out why it didn’t work on firefox. It hadn’t been updated in years, so something changed in firefox in the last few months.
I assume the Chrome version still works. I’m not installing it.