Have you tried Firefox 52 ESR? it no longer received updates, but it should work on XP (SP3 at least), and supports TLS 1.2, which almost every site should supp

Have you tried Firefox 52 ESR? it no longer received updates, but it should work on XP (SP3 at least), and supports TLS 1.2, which almost every site should support nowadays. It should work fine for a while until we gradually move to TLS 1.3+ exclusively, and there is no deadline set for that.