I'm sure that's a big part of it. The old-style extensions were so powerful because they could put their API tentacles very deep into the rendering engine. Moz

I'm sure that's a big part of it. The old-style extensions were so powerful because they could put their API tentacles very deep into the rendering engine. Mozilla paid a huge price for allowing that though - it was very difficult to change the behavior of many parts of the rendering engine without breaking extensions. Much of what you'd think was just internal implementation detail was actually API surface accessible to those extensions. The workarounds added a bunch of internal complexity. It really slowed down the pace of development. I get that some people mourn the loss of that style of extension, but dropping it was an important decision that should have happened much earlier. There were other issues with the old-style extensions (e.g. security) but making the pace of development uncompetitive should have been enough to doom it.