palemoon update required compilation, and this went on for over an hour:
65:27.58 Overall system resources - Wall time: 3922s; CPU: 0%; Read bytes: 0; Write bytes: 0; Read time: 0; Write time: 0
65:28.10 We know it took a while, but your build finally finished successfully!
100% on a Intel® Core™ i5-2400 CPU @ 3.10GHz (4 core)
This seems out of proportion for a Firefox fork aimed at slower computers.
You say that. Building firefox-opensuse-kde from the AUR took over 5 hours on this machine here, which has an Intel Core i5-8400 processor with 6 cores, and at the time, 8 GiB of RAM ─ it has 16 GiB now ─ which was all maxed out, plus another 8 GiB worth of a 10 GiB swap partition.
Unless you’ve got at minimum an 8-core/16-thread processor and at least 32 GiB of RAM, installing the binary AUR package is always going to be the preferable way.
That said however, palemoon-bin is in the regular repository. You don’t need the AUR for that.