Waterfox 6.5.10 can crash with eg YT pages due to an upstream issue.Also it can allocate huge amount of memory (30GB was observed) at times, within a few seconds.
For now pls revert to the previous version, Waterfox 6.5.9 when experiencing problems.
As an alternative Waterfox 6.6.0-beta (not yet supported of course) can be installed from the omniverse repository.
Make sure to first backup profile directory ~/.waterfox
artist