First, it is proper Netiquette to install viewing apps. So, do install viewers. Then, watch movies online.
Viewing Netiquette For Video
Popular video services have their own apps. Using a native applications provides better quality than browser viewing. Given, optimized for the content they display. Browsers may not play content according to optimal settings.
To start, Netflix, YouTube, and Amazon prime have apps. Next, YouTube comes installed on Android devices. Also, Netflix and Amazon are subscription services with desktop version. It follows, use the apps if you have the service.
Install viewing apps because they provide better experiences than websites.