I tried regular Firefox and nightly both show such usage. I'm mostly reading up on news, Twitter and browsing this site.
In my experience Android battery stats are largely worthless. I know for a fact that it produces complete nonsense quite often and shows high values for apps that are configured to force stop on exit and have no background permission.
I assume you have ublock running? Otherwise disabling background activity for it might help.
Also, that 40% figure is not a battery percentage, nor is it a percentage of battery usage from full charge, its the worst possible statistic that could have been used: a percentage of battery usage where "100%" is the total recorded battery usage of all things in the category you're viewing.
And no that isn't clear or well documented in any way.
There is this view which is much more useful, but im not sure how accurate it is either.
Another Tubular user! ๐
Of course it's in mAh - a nearly worthless unit for most use cases.
Why would mAh be worthless?
It isn't a measure of power. That's watt hours.
I hate whoever came up with using that unit instead of watt-hours. At the very least you could state the battery's voltage.
I think you mixed something up here. Nobody cares about the amount of power (Watt) an app uses, they care about the amount of energy (Wh).
If you take a look at your battery its got a Voltage (V) and a electric charge (mAh) value. If you multiply those you get energy capacity (Wh) but the Voltage isnt really important here as its always the same for most phones. In practice the mAh value is all that decides your batteries capacity (for normal phones at least).
So if your battery has 4000mAh capacity (when new...) and an app uses 400mAh then it has consumed 10% of a full battery charge. This all assumes that the phones measures things correctly of course but thats beside the point.
In practice showing mAh is the simplest way to figure out the energy usage of an app relative to your batteries energy capacity.
Battery usage depends a lot on what kind of websites you're browsing. Simple, static sites don't use much. Javascript heavy sites can drain the battery fast, especially if a script is misbehaving. Most sites these days have loads of javascript.
It looks like it's been using a lot of power in the background. You can try setting Android to restrict the background power usage for Firefox.
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