I had one of these white plastic iBook G4s. My next laptop was the very first “unibody” MacBook Pro 15”, bought from a Thanksgiving sale in 2008. I upgraded the RAM to 8GB and the HD to an SSD and it still runs great today. I stopped trying to upgrade the OS so the biggest challenge now is security. Thankfully Firefox has a long-term-stable version that still runs and gets current root certs for TLS.
I don't know. The iBook G4 had DDR 333 MHz PC2700 at best. The modern SSD of a Macbook M3 is about twice as fast in GB/s (2.5GB/s vs 5GB/s). The latency is likely worse, but at the same time the M3 has much bigger L1 and L2 caches (192KB*8 vs 64KB, and 16MB vs 512KB).
You’ll either need to give up GPU acceleration on the unsupported upgrade to post-Mojave, or lose the Firefox support later this year on the next LTS. I’m not happy about it.
