Edit > Preferences > Advanced > Encryption > and deselect "Use SSL 3.0" in the protocols area. I'm not too concerned about this sort of thing (if I was, I probably wouldn't be using Firefox 2 anyway), though I have just disabled SSL 3.0 because it looks like nothing uses it nowadays anyway.
Sure enough, that test website now says my browser isn't vulnerable to any stray POODLEs lurking in the interwebs (though I think the work involved in that attack would be far less than worthwhile for anyone looking at my internet data.
More so than that too, most web servers will hopefully disable SSL3 on their end. But also obviously as you mention,
Finally, that first web page you linked to doesn't work in Forefox 2 (it uses a later encryption method (probably TLS 1.2 or 1.1) that Firefox 2 doesn't support and for sume silly reason they haven't enabled TLS 1.0 as a fallback)
So if there's not a way to enable 1.1 or 1.2 then most sites are going to end up not working anyway. This is more an issue after the Snowden leaks because now more than ever are sites using HTTPS where as 3 year ago they wouldn't had unless they were a shopping/banking site. https://www.eff.org/https-everywhere/deploying-https (To be fair also, this is somewhat an issue with Dillo until it gets better HTTPS support http://www.dillo.org/FAQ.html#q12 )
As for those plugins. I'm not going to go through that web page, but the NoScript Download Page (https://noscript.net/getit) says under "Direct Download":
"Users of Firefox 2.0 and below are urged to upgrade their very unsafe browser. For those few who can't, latest legacy-compatible NoScript version is 1.10."
With a link to V. 1.10. So that's easy.
Yeah, at the very least having some version of Noscript would be a ton better than nothing. (thanks for that btw, I'll give it a try later)
AdBlock Edge is too new for Firefox 2.0 support, but AdBlock Plus which it's based on will work if you use the old V. 1.0.2 (https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/versions/?page=2#version-1.0.2). Though funnilly enough, the Firefox website is now so broken with Firefox 2.0 that the download link doesn't seem to work.
Actually, the more I got thinking about it the more I'd try to avoid any version of Adblock for DSL. Adblock can be pretty cpu/ram heavy on modern machines at times. I think just Noscript would be the way to go.
All in all, there's probably also a ton of unpatched browser exploits that Bon Echo is vulnerable to as well. That, along with it being pretty draining on older system with little ram compared to Dillo. Like, I can easily run the latest Firefox on another system I have, and it's just a 500mhz AMD K6 III rig with 512mb ram- yet if you have a 83mhz Pentium (which is my DSL rig) then Bon Echo chugs until you close it. I mean, I get Bon Echo was never meant to be more than what it is, but I'm just wondering if it's worth the hassle these days. (but don't confuse me in saying it should be straight out scrapped altogether, I'm just thinking outloud of all the difficulties).