Indeed, I do not experience it on my Samsung S22 Ultra, and I remember reading some article about how certain OEMs will change how Android manages RAM to try and improve the "experience" which results in weird behavior such as this.
There is an event when the app is not in focus and they can save their data to avoid it being deleted or the webpage reloaded.
Like a snapshot of the page.
IIRC MIUI has for quite a while been tuned very aggressively in terms of memory management. That is to say, it's probably not the browser but the underlying OS that is pruning processes to keep memory free when it really doesn't need to.
This ended up becoming a big issue with my OP7Pro where it would very aggressively kill apps causing them to constantly need to reload which would cost a lot of battery. My Pixel 7 does none of that and Firefox works great.
Firefox for Android straight up sucks. Sorry but it's true. It's heavy and slow with a bad ui. It basically has one and only one benefit. Add-ons. That's it. It's even worse on tablets. It's basically the same app but bigger. I bet Android users make up most of Firefox mobile users but they can't make a proper app.
Hey it's my first time interacting with a mastodon user on Lemmy. Wonders of the fediverse. If you live in the EU it's about to get better because they won't be held back by webkit anymore. Unfortunately only in the EU. So now they'll have to make two apps for iOS.
Edit: I forgot to add. Every web browser on iOS is basically just a skin on top of webkit because Apple doesn't allow it.
Do you have the same issue after rebooting your device?
Android's memory management may be struggling with a lot of cached resources in RAM that are being used frequently, besides Fennec. (Cached resources' memory space may show up as "available", but in reality this space is in use - run cat /proc/meminfo in a command line on your Android to see how much RAM is "free")
When this happens, Android pretty much sends memory warnings to apps as soon as they are moved to the background, forcing them to save the bare minimum data needed to resume, before they are killed by the runtime. Fennec in this case is just saving your active tabs, but not the form data within. This behavior cannot be changed
Only fix in this scenario is to reboot your device AFAIK
I also have a PoCo F3 on MIUI, FF sucks like you said, but the worst is that sometimes it drains battery. Even if I force close it, there is a background task eating the battery.
For instance my phone is at 80% at 10PM, I go to bed, at 6AM it is at 40%, battery status says that 40% of the battery was taken by FF during the night.