bug#59546: qutebrowser and icecat stuck in infinite browser checks (cloudflare) on applicable sites

["bdju" via Bug reports for GNU Guix <bug-guix@gnu.org>]

I have hit this issue before, but not in a while. I don't know for sure
when the issue came back as it only matters for the initial login or
visit of the offending sites, so if you manage to get past you'll be
good until your cookie expires or gets deleted somehow. I got logged out
of many sites in qutebrowser recently and was made aware of the issue
being back. I also tested in icecat where some sites I still had a
cookie, but I managed to find one with a browser check and it indeed
never completes (can leave it open hours or even more than a day).

Some sites to test with include:
https://www.livechart.me/ (must click login button, main page works)
https://www.gitlab.com/ (again must click log in to start the check)

Since this is happening in both icecat and qutebrowser with different
user agents and everything, I suspect a guix-related issue. I found that
at least one other person on IRC was also experiencing the infinite
browser checks. I use a few sites daily that are now unusable on my Guix
System machine due to these browser checks, so a fix would be very much
appreciated if anyone could figure this out.

guix version:
guix (GNU Guix) eb5e650e09dd096c066278918456f3e989f7b9d9
running Guix System as my distro
Issue first noticed (again) under a week ago, but could be older.
In the past I fixed it by spoofing a firefox user agent the same way in
both browsers, but it seemed like it was not working to do that anymore.
Currently I have both browsers set to default UAs again, also not
working.
There is also a relevant closed issue on qutebrowser's github:
https://github.com/qutebrowser/qutebrowser/issues/7208