I have a similar experience... around two years ago, both my laptop and desktop power supplies died (power surge), leaving me a pII-300... with which I had some "let's be authentic nineties" fun previously, so Win98 and Office 97. Except for the browser (lots of websites didn't even load on IE4-ish browsers), so I ended up with Firefox 3.x (the newest that ran on win98).

It actually took long times with 100% CPU to render web sites. And then further time to scroll them.

My observation is the same as yours: there is nothing better to discourage random web browsing than it being inconvinient. I could look up everything I needed to stay productive, I just didn't want to, because it was soo slow. (Having a smartphone + a non-networked computer seems to have the same effect, but with phones getting too fast nowadays, the difference seems to be diminishing...)