Argh. This is Microsoft's implementation of Javascript.
The time popup has to correct for the timezone of the browser, as it relies on the Javascript library to convert epoch time (how MRTG/RRD/Routers2 work internally) to human-readable time, in the timezone of the Target rather than the timezone of the client browser. Unfortunately these things dont always work.
There are occasionally problems with out of date Javascript libraries which have the wrong timezone settings (last year many countries changed their summer time rules).
The generated code is identical for IE and FF; the only difference is a slight rule change on how javascript sets the popup options. The code to calculate the time is the same. This puts the error firmly on the shoulders of MS, although that doesnt help you much. The only hack would be to make a browser-dependent time offset kludge in the generated javascript, but even that is not ideal as I use IE7 here and it works for me
(I test with firefox, IE6, IE7, and Avant Browser)Can you check that your workstation timezone and local clock are set correctly?