I'm using https://einaregilsson.com/redirector/ with a couple custom rules. Unfortunately, it appears the author has died (https://github.com/einaregilsson/Redirector#tribute), and the project is in a maintenance state. But it does exactly everything I need, and I disabled the auto-update, so I should be safe from any takeover attacks. Thank you, Einar.
Was going to mention Redirector too. Excellent tool/extension. Didn't know about Einar. It seems the next most prolific contributor has taken over maintenanceship. But, yeah, for time being works fine as is. (Didn't know tool was that old--has existed ~20y!--either.)
They should really update those links. Could be a coincidence but about half seemed to redirect me to a service that was discontinued or continued under a different name.
Ah I hadn't realised development is falling behind a bit (addon last released 6 months ago, though it's possible it doesn't need updating I guess)
Could just be the webpage to be fair, but it's not a great look.
After trying a few others I do think I was a bit unlucky with my first few tries.