Is javascript RSA signing safe?
If you implemented it well, and there is no MITM (i.e. use authenticated comm channel), then it is difficult to forge the RSA signatures (meaning you can use them safely).
However, in your implementation there are 2 other major factors that you need to consider:

One is the use of Javascript as a coding medium: there are many who consider Javascript to be a bad languange to use for writing security code due to some notable exposure to adversaries. I personally am not in that camp - if you take good care of securing your environment where you run the JS code you will be OK.
Also, there are some advantages of letting the user's browser do the work (and Java has its own set of implementation / management problems), this may be a prudent choice.

The second point is a major one: you selected “cryptico” engine, and we don't know how well the guy who wrote and modified the code behaved.
Some critical security routines there were modified by him, and this should ring a big red alarm bell over its usage. If you plan to use it for anything important, you need to pass the published code through a critical security/cryptographic review before usage.