[gnomewascool]

> There were operating systems which took the approach XPCOM has to extensibility, they're not doing so great

The Emacs OS is still doing well! :)

> "Mozilla did kill XPCOM" isn't a deviation from their stated intent.

The issue is that their stated intent changed over time, and their communication about their precise intentions was often pretty poor.

It didn't help that the Webextension transition came on the heels of the e10s transition (5 firefox versions separated deprecating non-e10s add-ons and disabling e10s add-ons), but with relatively little warning, which meant that:

1. Many people implicitly believed that once they adapted their addons for e10s, they'd be safe.

2. Many people put in a huge amount of work to adapt for e10s and then had to redo a large part of it to convert their add-on into a webextension.

3. Some people put in a huge amount of work to adapt for e10s and found out that their work was pointless because their add-ons couldn't be converted into webextensions.

From a technical point of view, much of Firefox's XPCOM/internals were actually sufficiently stable post-webextension (57) that old e10s extensions could have continued to work with little changes. (e.g. VimFx continued to work with minimal changes for ~30 Firefox versions, on Nightly, with very slight hacking. AFAICT it still continues to work, with slight changes, but now with major hacking to get it to actually install.)