fps is not a part of UX for all apps. Usability needs to take into consideration the hardware features available. If you're running on 1 ARM CPU with 128mb of R

fps is not a part of UX for all apps. Usability needs to take into consideration the hardware features available. If you're running on 1 ARM CPU with 128mb of RAM with no graphics hardware acceleration whatsoever and you need to present hundreds items to the user such as a contact list and you know the hardware can't cope with scrolling large tall DOM elemements then you opt to use some flyweight pattern or you simply paginate the damn thing. Don't do the scrolling, offer another way to peruse the data. You can't approach low-spec hardware with UX and solutions from high-end devices. Remember progressive enhancement. Also the phrase: Try scrolling down a list of items on a Firefox OS vs a iPhone 6 and tell me which one has the better UX. Is silly. Firefox OS was not created to compete with the iPhone. We're talking about low-specs in here. If you're making this comparison then I would suggest that you look on the objectives of Firefox OS and the devices available. They are not similar to iPhone. The fact that people think that the epitome of UX is "fast scrolling lists" or fps shows what is wrong with this industry. UX is how you get a positive user experience given the constraints you have and not how to squeeze every single fps out of every single computing core. If you're in a low-spec device, you restrict animation and scrolling tall elements. You pre-cache and pre-render whatever you can. You find another UI scheme to use besides "hamburger menu + scrolling tall thing". Don't mix fps to how responsive your app is. fps is how fast it can blit stuff to screen, thats not the same as how fast it can handle user input. The A/B Testing helps with creating the UI for low-specs.