In regards to XP browsing, Pale Moon's developers decided it was a good idea to block out anyone using a user-agent string below NT 6.1, or containing the word "Mypal" along with some sort of anti-spambot protection (due to some older scraper/bots typically using ancient useragent strings such as IE6), from their addons site.
Apparently their excuse was that they're (roytam1/Feodor2) using up so much - conveniently, without any actual statistics of any sort - resources of PM while giving nothing back to the mainline project, and people are jumping to PM's forums asking for support for these unendorsed forks (as if that has any blame related to the developers), which according to them, constitutes abuse.
It's also not the first time they've pulled this garbage, either. There was the time with the BSD install script, as well as the Slackware builds. What's ironic is that Pale Moon appeals rather highly to users of these forks (especially given most users of anything past Vista won't give a damn about customisability) and users who are typically on lower end hardware... and they're literally calling them abusers of the original project? I think there's some very narcissistic developer attitudes going on there, tbh.
That said, given the state of the Modern/Consumerist Web that forces you to load 322 elements before you even see one line of actual content start to load, and keep JS on (unless you want to spend ten minutes trying to make it work without it client side), don't even bother using XP online, there's just no point. An 8 years old laptop with a low end processor would struggle, let alone something that likely lacks SSE2 support and has below 8 GB of RAM - it's a pretty sorry state really, and one that no one will ever solve while the more Chrome gains share, and the rest just keep on copying it as FF has done since 2008, while even the one viable choice is poor due to the attitudes of its developers being a rather possible putoff for some.
I swear, 2016 and beyond really was the death of the Internet, and it's ultimately everyone younger than us who's gonna suffer in the long run.
(Thus concluding a pathetically long, kinda off-topic, ranty post. Hi btw.)
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