For Mozilla based browsers there are plugins, mainly uBlock Origin or uMatrix (I prefer and use uMatrix) and/or NoScript. These block third party analytics and external servers by default. Webkit based browsers have some old plugins as well, not sure any work anymore.Exactly. I was surprised at how much I could actually run on it. Sometimes at the bottom of Interwebs, you can see all the content that needs to load, and some websites are totally swamped with content that you never knew you'd "need" for certain web pages. (Which is unrelated, like you said).
I wonder if I can block things on my iBook G4, and get that running on the internet. It is running very slowly at the moment. It does work, but the lag is extreme. Imagine what it would be like on it if all that "content" was blocked...
There is a System Preference that will block websites system wide. Forgot what it was called at the moment, but that's also pretty old. However, it works across all browsers and anything that connects to the internet. It might only be for PowerPC though.
Lastly, there is your hosts file. You could painstakingly place each and every one of these sites you want to block inside your hosts file. That'd take knowing the sites and a lot of time and effort - but it could be done.
As to your iBook's lag, well honestly this is why. Unlike, more modern Macs, every webpage gets translated by your CPU. It is not handed off to a GPU or some other secondary processor. And until your CPU is done processing it, system resources are limited. The trick in web browsing on old Macs is to limit the amount of time the CPU spends processing a webpage. The faster you can get it processed, the faster the CPU returns to idle and the 'quicker' the Mac appears to be.
With Mozilla based browsers there are tricks we can do. Addons and about:config mods that will speed things up. I used to maintain a thread in the PowerPC section about all that - but it got superceded by this project: https://forums.macrumors.com/thread...xpep-for-a-faster-firefox-tenfourfox.2209108/
There are other tricks, such as putting your cache, profile and the browser itself directly in ram by creating a RAM disk. You're never going to get something as fast as the newer Macs but it's better than stock.