I think you should probably try to get your browsers upgraded. Not just for the P5.js editor, but for general sanity.
But if for whatever reason you can’t update them, it’s worth noting that the P5.js web editor isn’t strictly required to edit P5.js. It’s perfectly fine to use a basic text editor, or the Processing editor itself, to edit P5.js code.
Shameless self-promotion: here is a guide on different editors that can edit P5.js: