MetaMask's browser support policy is to support:
- The last two years of Chrome stable releases
- The current and previous Firefox Extended Support Release
We try to support browser forks as well (aligned with supported Chrome/Firefox releases), but we don't actively test them.
Additionally, before bumping our minimum supported browser versions, we should always notify users in the application first. Otherwise users of older browser versions would unknowingly get stuck on old MetaMask versions, even if they had automatic updates enabled.
We have a home screen notification already for this purpose. All we need to do us update the OUTDATED_BROWSER_VERSIONS
constant in the release prior to the minimum version bump, and all affected users should be notified in-app.