Define a manual QA process and add e2e coverage for older browsers

[seaona]

What: define QA manual process and add e2e coverage for older browsers. cc @Gudahtt

Oldest versions we are supporting:

• FireFox: 68.0 https://github.com/MetaMask/metamask-extension/blob/develop/app/manifest/v2/firefox.json#L5
• Chrome: 66 https://github.com/MetaMask/metamask-extension/blob/develop/app/manifest/v2/chrome.json#L7

How: as per @pedronfigueiredo 's suggestion, we could investigate whether Browser Stack fits our needs.

Relevant related issues:

• https://consensys.slack.com/archives/GTQAGKY5V/p1669860469331419
• Notify users that we are dropping support for their current browser https://github.com/MetaMask/metamask-extension/issues/16283

[danjm]

Three results needed to close this ticket:

1. Documentation on manual QA process for older browser versions.
2. Automation for a nightly run of existing end-to-end tests on older browsers. We will need to disable some tests, because older versions of webdriver do not support all current extension functionality

TODO:

• [ ] Identify a minimum viable set of tests to run nightly against older browser versions. As part of this, review past bugs where we broke older browser versions
• [ ] Add automation to lint against using apis that don't work in older browser versions

[danjm]

Blocked by https://github.com/metamask/metamask-extension/issues/17849

[danjm]

Decisions to be made:

• do these e2e tests with our current set up?
• use browser stack?
• what tests do we need to run on the older browsers? what subset of the tests?
• evaluate impact on pipeline speed (time for circle ci runs), and consider whether the costs of having this on every CI run outweight the benefits. We may want to run these tests at some frequency different from every CI run, for example we could do it only on merge develop, or on a schedule.

Acceptance criteria:

• documentation on how to run the tests on older browsers