0.99.133-beta, macOS 15.4.1
Same problem here. About 20 tabs open, most are sleeping. Bitwarden (Firefox) is only extension. Browser becomes sluggish after a while. Some tabs, especially YouTube, consumes a lot of memory, but both CPU and memory usage is within what I would call normal. I tried to flush the cache, it didn't help.
Edit: I installed Bitwarden for Chrome instead of the Firefox version and Orion has been behaving well so far. As others have mentioned this might be an extension issue.