I have just switched from Orion to Vivaldi partially as it seems to use less memory.

I suspect this is because I use several profiles amd each one in Orion is in effect a copy of the whole Orion browser whilst in Vivaldi less things a re duplicated. Or possibly my style of when to close things works better wehn an app has many profiles like Vivaldo or Safari rather than each profile is an app like Orion or Firefox.