> I remember that the introduction of the new WebExtension API to replace the existing extension system
Actually, the existing system is still alive and kicking, since the internal components of firefox, above a C++'ish core, are (more or less) like traditional extensions. It's just that you're not allowed to load your own anymore. In Thunderbird they've created a loophole of sorts, so we can still load normal extensions.
> It was a painful transition but very much needed.
On the contrary, it was the opposite of what was needed.
> Now extensions don't clash with one another.
1. Many important extensions simply aren't allowed to run now.
2. They don't interact, so in particular they don't clash.
> The browser code can be modified more freely without impacting extensions
1. It still impacts the internal extensions.
2. Since webextensions can do very little, they're not impacted by much.
Actually, the existing system is still alive and kicking, since the internal components of firefox, above a C++'ish core, are (more or less) like traditional extensions. It's just that you're not allowed to load your own anymore. In Thunderbird they've created a loophole of sorts, so we can still load normal extensions.
> It was a painful transition but very much needed.
On the contrary, it was the opposite of what was needed.
> Now extensions don't clash with one another.
1. Many important extensions simply aren't allowed to run now.
2. They don't interact, so in particular they don't clash.
> The browser code can be modified more freely without impacting extensions
1. It still impacts the internal extensions.
2. Since webextensions can do very little, they're not impacted by much.