CRL made by xca isn't compatible with Firefox. Attempt to import CRL directly into Firefox leads to Checking Error Code:ffffe009. It's known behavior of Firefox (maybe some other programs) - you can find some discussions in Google.
The same CRL can be successfully imported into Windows certmgr. So, the CRL is commonly valid, but Firefox obviously expects other format of CRL and doesn't support other formats.
I suggest to add option to make CRL compatible with Firefox.