bug 534079 required we change the '#define IMPLEMENTATION_VERSION' in toolkit/components/url-classifier/src/nsUrlClassifierDBService.cpp
We updated the 220.127.116.11 release to '8'
The 1.9.1, 1.9.2 and 1.9.3 versions are at '7'
The next version number to use on 1.9.3 + is '9', so it will jump from 7 to 9
There probably will not be another 1.9.0.x release after 18.104.22.168. If there is, just increment +1 trunk's version and increment trunk on subsequent releases (that have changed) to +1 the highest revision.
This most likely will not be a problem.