I assume you're talking about the Minecraft Classic Timer userscript.
First you want to install an extension that supports userscripts. Popular examples are Tampermonkey and Greasemonkey (the latter is Firefox-only). I believe Chrome supports userscripts without any extensions, but I've never tested it.
Then you simply follow the link and click the "Raw" button. You should get a pop-up asking you if you want to install the userscript. Once it's installed, it's completely automatic, and will show in the top-right on classic.minecraft.dev.
For Livespilt, you should turn on global controls, then press 1 on the Number Pad. For the script, it happens automacically if you follow birj's steps.
Hello
Hello Classic runners,
Recently, our run queue has gotten a little out of hand, with runs 47 days old still pending. I want to apologize on behalf of the mod team, as that is way too long for runs to be pending.
To be honest, the mods have been really busy with other more important t
