My experience with FireFox and YouTube has very much not been this. YouTube works perfectly for me on FireFox. I would check your config/addons and see if there is some setting that is causing errors on YouTube.
To me it seems like their passion drove them to learn as much as they could. They knew enough to get the job done, but not enough to know that they "couldn't do" the things they wanted to do.
More experienced devs may have thrown out a lot of the ideas the Half Life team ended up implementing as "too time consuming" or "practically impossible". Valve's devs at the time weren't experienced enough to make those assumptions, so they just worked their asses off to figure out how to do it.