The following filter options can't be translated into DNR rules:

strict1p, strict3p: whether a network request is same-origin as its initiator
Entity-based values for domain= filter option (webextensions #394)
redirect-rule=: the DNR API does not support redirect-if-blocked concept (webextensions #493)
Click-to-load embedded contexts through redirect=click2load.html filter option
Regex-based removeparam= modifier filter options
Exceptions for all modifier filter options are not possible
    Workarounds exist for removeparam= and csp= by carefully tuning the priority property.
Many very useful regex-based filters used in uBO are not allowed, or are rejected by the DNR API (webextensions #344)
replace=, can't modify the response body (full support is only possible with Firefox MV2)
ipaddress=, can't use IP address as a condition to block/unblock (full support is only possible with Firefox MV2)
urlskip=, this requires programmatic steps to extract a URL from another URL (partial support, for strict-blocked pages only)

aside from that it is somewhat better than default ublock but that's a pretty big list of issues.