Disney Plus on Firefox

I have been watching Disney Plus on an older Dell Optiplex with a Core 2 Duo that has about 4 GiB of RAM. It does a fine job, actually. The issue I seem to be having is that after using it for quite a while, it starts to eat into swap space. I use this same machine for streaming from YouTube, Netflix and my local Emby server without any issues. I am guessing Disney Plus is perhaps doing some excessive caching. To solve this I close out Firefox periodically to flush what seems to be a memory leak.

Has any one else had similar issues and is this exclusive to Disney Plus? Any thoughts as to how I can mitigate this? Otherwise, I just want to see what other experiences are out there.