Sprite particles on avatars became blurry on beta when sprite textures have mipmaps and mip streaming enabled. Disabling mipmaps not the best solution and not always possible for old content. Textures used by Particle Systems should use highest mipmap quality when possible.
Perhaps Texture2D.requestedMipmapLevel can help?
Attached two screenshots, one from Live and one from Beta (blurry)
Example avatar ID with this issue: avtr_8b5d44b2-5aec-4176-afc3-93ead7dd183f