As someone maintaining Gecko in a large distribution for years, I can tell you the vast majority (if not all) of the cases like "Site X works in Firefox 3.6 over there but not here" nowadays come from the fact that here is not Firefox but something named differently (guess why). Not from patching.
There was a time when we had problems, and they weren't due to patching, but to enabling an unsupported feature, namely the pango backend, at a time where both backends had their drawbacks.
Posted Jul 1, 2010 9:12 UTC (Thu) by oak (guest, #2786)
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Yea, there are quite a few www-sites that check browsers by the name they report and refuse to work if browser's name isn't one they explicitly check for.
(I've recently seen this in one company's internal SAP www-service and many years ago one large scandinavian bank had this kind of a beginner mistake on its public site main page, it gave a completely blank page e.g. in Konqueror...)