Firefox just used almost a GB by just opening it! I only typed a Google search, and the next moment my phone tells my I'm out of data! Note that this is foreground data, not background data. I googled and found answers about media playing in the background, but I haven't watched anything recently, so no streaming link should be active. I installed Ublock origin so I hope that might help. Attach is my Firefox data usage for the past week of barely using it, except for an occasional Google search.