how ton install and get updates

You need a newer operating system or perhaps even upgrade your Mac first.

To run any Firefox version past 78.#esr you'd need to upgrade from your macOS 10.10 to at least 10.12 to get the still updated legacy 115.#esr version that is gonna be supported for a couple of upcoming months, but to run the current release versions like 150.x+ the minimum system required is macOS 10.15 and newer.