While it is possible to compare the same browser across two different version of jQuery, it's pretty difficult to do so: you need to manually "extract" the slivers from the two different bars and compare them visually, which is difficult and imprecise. I think it would be more useful to have one pair of bars for each browser (old vs. new jQuery version), and then a pair of bars for "total over all browsers" (old vs. new jQuery). That is slightly more verbose, but more useful too.