What's the best way to keep API usages simple but working for both MV3 and MV2 (due to Firefox dev)?

[Destroy666x]

I'm new to browser extension development. The problem:

• I'm using MV3 for obvious reasons
• Firefox dev mode doesn't work with MV3
• Firefox MV2 has different functions for certain things

So e.g. browser.action.setBadgeBackgroundColor throws an error in Firefox because it wants browser.browserAction.setBadgeBackgroundColor. This makes the extension not easily testable on FF. I've seen the GH/FF issues regarding this and it'll likely take a while to have dev mode support FF MV3. I don't really want to do (browser.action ?? browser.browserAction) kind of workarounds.

What would be the best solution for it as of now? I've seen some polyfill got removed in recent major WXT version. Would installing it help? Would it introduce any issues? Or is there some other automated way that polyfills or does something to solve the MV3/MV2 testing incompatibilities?