First, the FRM-93240 problem is a known issue that has been corrected in an upcoming patch. For current versions (126.96.36.199 and 188.8.131.52) a tempory patch is available. Contact Support and refer to Bug 16567961
The second part of the issue is that adding "DEBUG" to the url will only enable servlet diagnostics. In most cases, this is of little value unless you are trying to troubleshoot a networking issue or session handling issue, or maybe a performance issue. The tracing which is found in EM can provide granular diagnostic information about a running form. This is not the same as servlet debugging. Refer to the document for details.