I wanted to know wheter it makes sence to disable Mozillas fetching service for privacy reasons.
I also noticed that it is impossible to revoke location permission from microG. What is the reason for that?
In the permission list microG is requesting my location even after disabling all microG features and location services.
Only if you think Mozilla is collecting something you don’t think they should. If you don’t want to contribute to the service then sure.
From what I read the MAC address of a Wi-Fi device may be collected (BSSID, not the SSID). If you do not like that then toggle off “Use Wi-Fi”.
In Developer Options of the phone you can turn on “Wi-Fi-enhanced MAC randomization” to minimize the concern but that feature relies on a router that supports that feature.
Far as I know no device or similar data is shared when collecting Cell data.
You can get an overview of what MLS does from Wikipedia, which explains a lot more than Mozilla’s own site.
Mozilla Location Service - Wikipedia
MLS - Overview
On old phones probably the option is also present and you expect it to work but it isn’t because AFAIK the driver blob also has to support it. Google introduced it with Android v8.0, “starting with Android 9, you can enable a developer option”