i cant install this mod via the mod portal and it says its been updated 3-4 days ago.. have there been some update to vanilla that render it outdated?

Factorissimo2 is compatible with Factorio 0.14 and 0.15. If you have 0.15, make sure you're running the latest experimental version (version 0.15.10).

Does downloading the mod not work? That probably just means that the mod portal is down, it's been having issues lately. If you can't install it using the ingame launcher, try going to the "Downloads" tab and getting the proper Factorissimo2 download for your version (either 2.1.5 for Factorio 0.15 or 2.0.4 for Factorio 0.14), then putting that into your mods folder manually (Use Google to learn where to find your mods folder).

i got 15.10 and the install button never lights up/activates and ive installed other mods without a problem

EDIT: nvm it works again

The mod portal has been acting up recently. Manually download and install, and everything should be fine.