Temporary solution to some of the slowdown issues is to use uBlock Origin to block the domain 'robohash.org' (used to generate the default avatars)

You can do this by:

1. Right-clicking on any robot avatar
2. Choosing 'Block element'
3. Deleting everything after 'robohash.org'
4. Pressing the 'Create button'
5. Refreshing the page

Hopefully @BonfireBuilders will swap out the default avatars soon!