Not sure what's going on. I can reproduce in Firefox with DDG and Google.
Edit: it only happens for me in Firefox with particularly locked down settings. It turns out McMaster is not actually inserting a 3XX redirect, it is happening via the history API.
As I updated elsewhere: upon more research it seems if you do not send a Referrer header, McMaster inserts a history entry using the history API. I can make it work/fail by tweaking Firefox network.http.referer.XOriginPolicy. It's interesting that McMaster is the only site I use in 2022 that has a problem with it.
Edit: it only happens for me in Firefox with particularly locked down settings. It turns out McMaster is not actually inserting a 3XX redirect, it is happening via the history API.
As I updated elsewhere: upon more research it seems if you do not send a Referrer header, McMaster inserts a history entry using the history API. I can make it work/fail by tweaking Firefox network.http.referer.XOriginPolicy. It's interesting that McMaster is the only site I use in 2022 that has a problem with it.