Vita firmware 3.73 “blocking” Modoru was only temporary after all, and basically a false alarm.
Developer SKGleba has released an update to the popular downgrading tool (originally developed by TheFlow), allowing it to support the latest PS Vita firmware.
The developer adds that this latest Vita firmware only seems to change something related to webkit (this might be a vulnerability patch, but not one that’s used in h-encore2).

With h-encore2 and Modoru both confirmed to work with Vita 3.73, it now feels safe to upgrade to that firmware if you were already on 3.7x. Users of former firmwares, running on the trinity or h-encore exploits might consider staying there.
Download Modoru 2.1 (supports PS Vita 3.73 and below)

You can download Modoru 2.1 from the developer’s github here.
Source: SKGleba