The short answer: Yes.
The long answer:
QHD (2560x1440) contains four times the pixels of HD (1280x720 or 720p) while UHD (3840x2160) contains four times the pixels of 'Full HD' (1920x1080). So, while it will display content from a Firestick or Roku, the devices will only display the highest capability of the display. Additionally, this display will require external speakers or headphones to be attached to it for audio playback.
In my opinion, if you want a 4k display for those devices, get a 4k TV as the price is similar to this Monitor. As a monitor, I love this one and use it daily at my desk as a secondary display.