There is no built-in web browser for the Roku. Easiest way is to either use an HDMI cable and a laptop or to wirelessly mirror your laptop/tablet etc. Basically, these two methods allow you to mirror and cast content to your TV either through the TV itself, or through the Roku OS depending on chosen method.
Different methods for different OS (Android, Apple, Windows, Linux, Mac). Personally, I have an extra HDMI cable at the TVs that plugs into laptop (then change TV Input source to that HDMI), in order to stream online content/mirror or browse the web, in your case, whenever I have difficulty casting online content wirelessly to the Roku.
For the most part, I use the Web Video Caster app and the accompanying Web Video Caster Receiver Channel available from the Roku Channel store for most of my casting.
Hope that points you in the right direction.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
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