Do you still have the Google search engine added? I always fully remove it, since Searx pulls from Google anyways, I don't really see the point in keeping it.
There's no reason not to leave it alone... though choosing a better default is advisable.
There are many times when SearX isn't a good solution (though SearX or SearXNG are a great default)... Your answer is 'popular' because everyone hates Google. But also problematic, because it will lead to folks trying something else and then just going back to the best one.
Happened twice ~6 months ago, even though I've removed Google from search engines.
After that it never happened again. It's annoying but it happened only a couple times so it's not a big deal for me
Maybe something they're doing with their custom build of Firefox? You could switch to a different Arch repo just for Firefox, or Snap/Flatpak versions or install directly from the Mozilla build.
I use Mint, and use the Mozilla PPA's Ubuntu builds instead of the Mint ones as I had some minor annoyances. Not sure if it's a good idea to go down a Deb route on Arch though? Not something I've tried. I don't think Mozilla maintains an Arch build themselves?