I have a similar problem when I use the package search engine that is built into qBittorrent. When I select a package & then hit the Go to description page button, which should take me to the relevant web page via my default browser - Pale Moon. Instead nothing happens. Pale Moon has never worked for this though Firefox always did? I don't get the slow down though (my machine has a powerful i7 CPU & lots of RAM, which may hide that side of the problem). I'll give this a look now & check it out with htop & see what it tells me.
OK, I just checked & low & behold, it worked! Pale Moon opened up the URL when I selected the Go to description page button.
Looks like a Pale Moon update (or qBittorrent as there was a big update not long ago) has fixed the problem.
Sorry for wasting your time loupe, though thanks for posting as you caused me to discover that the qBittorrent / Pale Moon problem is now gone.