Since you are sharing anecdotes, let me join.
For me FF has always been extremely stable, and I too regularly keep 100+ tabs open, on much more limited system resources. It is so stable that I’ve completely disabled history saving, and if there is something I want to read later I just keep the tab open. Never had an issue.
Tree Style Tabs also pushed me to have many tabs, because now I can actually organize those that I’ve opened and find them later.
It could be an issue with the codecs (browsers are usually pretty limited in what they support). You could try to use a client like Jellyfin Media Player instead. It bundles libmpv, so it plays almost any video format there is.