Add test for the FlowCrypt for Thunderbird implementation

[martgil]

Description:

In my investigation, there's not much option for testing Thunderbird mail extensions within the Thunderbird Mail Client. So to make our progress in Thunderbird mail development reliable, test must be added, emulated and performed in puppeteer.

Reference: https://www.zenrows.com/blog/puppeteer-user-agent

[martgil]

cc: @sosnovsky

[sosnovsky]

Hmm, I'm not sure that changing user agent will make it possible to test Thunderbird implementation, as browser environment will still miss some properties and methods specific for thunderbird (like browser.composeAction, browser.messageDisplayAction etc)

[martgil]

Yeah, you are right @sosnovsky. Oh my. It's not easy to add test for Thunderbird.