Firefox has issues currently on M1, as well - uBlock Origin won't load, for example. Thankfully, that particular issue is fixable by disabling javascript.options.wasm and javascript.options.wasm_trustedprincipals in about:config as a temporary solution.
I fully expect these to be fixed, but it's clear it's gonna be a few weeks/months before everything runs right. If I were a non-technical user, I'd be returning it for an Intel Macbook.
The 1Blocker extension can be disabled as a temporary fix, and crucially, the ad blocking functionality does _not_ have to be disabled.
https://twitter.com/1blockerapp/status/1329744152150626304?s...
In the meantime, disabling the 1Blocker Button extension in Safari > Preferences > Extensions and restarting Safari fixes it. It won't affect how our app blocks intrusive content in Safari since 1Blocker Button only provides quick actions to the main app.
I have had Safari open for 23 hours on my M1 MBP, and it is using ~800mb of memory right now. Extensions are the most likely culprit.
edit: https://twitter.com/hondanhon/status/1329132372034347009