from https://support.mozilla.org/en-US/kb/built-in-vpn

Understand the 50 GB data limit The built-in VPN includes a 50 GB monthly data limit. Firefox will notify you as you approach the limit When you reach the limit, your VPN status will change to paused VPN protection will be unavailable until your data resets Your data resets at the start of the next calendar month. If you need more data, you can subscribe to Mozilla VPN for unlimited usage.

To clarify, does the regular Firefox browsing just begin once the limit is reached? or would I have to use a different browser until the monthly reset?

To clarify, does the regular Firefox browsing just begin once the limit is reached? or would I have to use a different browser until the monthly reset?

You can still use the Firefox web browser, just that you will not be able to use the built-in VPN until it resets.

There is a whitelist feature on road-map as that could be an option so you only use the built-in VPN for specific sites instead of all sites and not use up the 50GB data as quickly each month period.