[hpbd]

All extensions are open source. Just download the xpi/crx and decompress. Doesn't help much unless you are willing to read all diffs, or never update them (and be exposed to bugs which could lead to other security issues.)

[bastawhiz]

You're right, we should never install software ever again unless we wrote it ourselves.

[Grangar]

You could (and should) minify JS for builds, which essentially renders it useless for editing purposes. Heuristically you could still find parts that phone home and disable those but getting further than that is going to be a pain.

[amingilani]

You're confusing 'source available' for 'open source'. Source available is where you can look at the source but don't have any right to do anything with it.

Open source is libre software.