In-browser tests are inherently slow, but since commodity hardware is insanely cheap nowadays there is no excuse for not running all these tests in parallel on multiple machines and dramatically speeding up your feedback cycle. This is exactly what Selenium Grid is about.
You do not even need to build or purchase an expensive server farm: in our experience a couple of Mac Minis or Linux Boxes can go a long way and help you keep your build under 10 minutes.
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