For those of you on rooted and custom ROMs, now you can easily update to the latest L900VPALJC firmware (with Multi-window) by flashing a zip file in TWRP Recovery.
There’s two versions of the ROM, one odexed and the other deodexed. I recommend using the Deodexed version as you can install mods like all-app Multi-Window. Odex version is more stock, you can use that if you are trying to unroot your phone back to completely stock.
Download and flash in TWRP:
Download L900VPALJC Firmware rooted Deodexed