avi45003, if you make a change to the html and then reload the
browser, try cmd+shift+R instead of just cmd+R, or disable the
cache temporarily. If the change is below a certain threshold, the
Firefox caching system may become confused. I notice this myself
when changing html files. You can also change
browser.cache.check_doc_frequency in about:config to 1 to make
checking for changes more strict.
If that doesn't solve it, can you give us an actual example
website that exhibits this problem? I'm sure it would have to be
Mozilla's bug (not ours), but without being able to reproduce it,
it's hard to say anything.