I loaded a page containing a: <script src="...js" =""></script> statement. The Console reported an error in the .js file. The line number was past the end of the file. The code it was complaining about was not in the file. The cache contained an older, longer version of the js file. When it read the new one, it updated in place, but it failed to correctly set the length, so the old tail was pinned onto the new file, causing a compiler error.

This'd be bug 79983 that you're seeing. It happens for any uri, not just relative ones. *** This bug has been marked as a duplicate of 79983 ***

VERIFIED: same problem