Firefox Updates and other mysterious downloads

[amethyst]

So, I've been using Palemoon all along but checking Firefox out now. I've noticed that after a few minutes online something (unknown) inevitably will be downloaded when using Firefox EVEN AFTER I HAVE DISABLED ALL POSSIBLE UPDATES in about:config (and there are a lot of things enabled for updates by default). So, what's going on here and what data is being downloaded? Do you Firefox users just accept this behaviour, ignore it and just tolerate this? Do you notice this and check your online data transfers? This is the kind of thing that bothers me, data received and you don't know what it is and don't have any control to stop it.
Edit: This behaviour now starts immediately when I start the browser. What the hell is this? Is this common behaviour for Firefox?

[williams2]

One thing that Firefox does, is it down loads a file to /tmp/ named tmpaddon.

It is a .zip file. If you unzip it and look inside, it is Widevine for unencrypting and playing drm videos.
tmpaddon is about 6MB.

[amethyst]

Thanks, the download was more than 10MB. In my version of Firefox 2 folders were created in /tmp but it didn't contain anything and I didn't see a zip file anywhere. So, I suppose the necessary was downloaded to the mozilla folders in /root because after restarting the download didn't occur again. I will be monitoring this though.....

[xenial]

I know firefox will issue GET requests for the google safe browsing downloads and also for certain hidden extensions.
I had to uninstall the latest pale moon v30 last night because the cpu usage was unacceptable even for just a window being opened plus all the themes etc were disabled.

I replaced it with librewolf which is a good alternative to firefox with a lot of the phoning home removed or disabled.