This PR updates our minimum supported Chrome version from 63 to 66, so that we may use the `AbortController` browser API without polyfilling it.
Our minimum Firefox version supports the `AbortController`, but our current minimum Chrome version (63, released in December 2017) does not. Chrome shipped the `AbortController` in version 66, in April 2018. We have determined that an extremely small number of users are on Chrome 63 < 66, and that this change is therefore acceptable.
Firefox v68 is the _previous_ Extended Support Release. We are
increasing this because our current minimum version doesn't support
async iterators, so some of our dependencies cause the extension to
crash.
Our metrics show that usage of Firefox versions older than this is
quite low (under 0.7% of Firefox users in the past month). These older
versions are also _very behind_ on security updates. Using the Extended
Support Release also makes it easier for us to test the minimum
version, and ensure our extension remains compatible with it.
Relates to #6805
The Chrome minimum version has been increased from v58 to v63. We found
that we had very few users on versions below v63, and v62 is
incompatible with our SES lockdown dependency.
This also makes us compatible with Object rest/spread syntax, so we
might not have to transpile that anymore. I'll revisit that separately.
The minimum compatible version of Firefox has been lowered from `60.0`
to `56.2`. It was originally set to `60.0` because that is Firefox ESR,
which currently the minimum Firefox version with security updates.
However Waterfox is based upon Firefox `56.0`, and has backported
security fixes from the ESR release.
This change in minimum version requires no additional transpiling, and
doesn't affect any browser APIs we use.
It does introduce one additional warning in the `addon-linter` about
Firefox for Android `56` lacking support for browser action popups.
However there is no version `56.2` of Firefox for Android, so the
minimum version remains `57` in practice (which does support browser
action popups).
Babel 7 moved to a new configuration format, and they've scoped all of
their packages under `@babel/`. This brings MetaMask in-line with
dependencies we use that _already_ use Babel 7, and it eliminates a
few unfortunate edge cases that can prevent dependencies from being
correctly transpiled.
