99% of sites (well, except for very simple ones with text) that I open in FF52 already work absolutely incorrectly. And already more than 10% work incorrectly even in FF94, which is only 1 year old! So your optimism about FF52 is not appropriate. Machines under XP, if you do not take into account the unsafe clones of chromium and ff of newer versions from the Chinese and all sorts of homemade ones, under XP, are already useless for the Internet for like 2-2.5 years for sure. In about 1-1.5 years, the same fate will befall W7-W8.1 (although the crooks from M$ and Google could have made it to 2025, especially since W7 still receives paid updates, including for the US Department of Defense - and this is taxpayer money, by the way, which means that all these updates must be available to at least all US citizens, as well as citizens of other countries where government agencies still pay for such updates).
I personally use XP only for a projector and music on an old computer, because, there everything goes smoother and without friezes, as in W7 (this is clearly visible if you start a movie in XP and W7 in the same video player with the same video card driver version - on XP, camera scrolls in scenes are smoother, about sound and speech no, XP absolutely rules here in terms of system latency and the likelihood of problems in playback, I somehow wrote about it in detail in the topic for news about chrome under W7 support end). Otherwise, XP (especially since it is also dramatically worse than WS2003 - the latter at least has support for GPT and disks larger than 2TB, plus memory support for more than 3GB and a normal TCP/IP stack with faster SMB) I have long been like a working environment not interested.