Sightly older version of Firefox here (140.x) on Debian Linux, no issues.
Maybe you have a browser extension that isn't playing nice? Try disabling extensions / maybe a private window & see how it goes.
Or if you're on Windows maybe you have anti-virus/malware software causing weirdness.
EDIT: Could be worth running memtest86+ or similar to rule out any RAM issues, wondering if you're just seeing crashing whenever you use software that starts to use more memory.
Probably not... but it might depend on what you're actually attempting to do.
What is port 6881 in qBittorrent? Is that a proxy port that qBittorrent is using, or are you referring to something else?
And what is it you want to do with the open port on the RPi?
The reason I ask is that qBittorrent does not have any support for incoming bittorrent connections when using a proxy. In other words the qBittorrent Listening Port is ignored when you put it into Proxy mode. Using a proxy in qBittorrent means never having an open port for incoming bittorrent connections, you're always firewalled / not connectable in that configuration.
If that's what you're trying to do it won't work but maybe it could work in a future update eventually.. if you're trying to do something else you may want to expand in your post (?)
e.g.
https://github.com/qbittorrent/qBittorrent/issues/21134
https://github.com/arvidn/libtorrent/pull/7726
https://github.com/arvidn/libtorrent/pull/8003
PS - Some other communities you can try
!qbittorrent@lemmy.dbzer0.com
!qbittorrent@lemmy.ml
!piracy@lemmy.dbzer0.com