TYPO3 Core

Indeed, this could be a problem. Please see http://allinthehead.com/retro/102/the-times-they-are-onchanging - it's not only a concern of TYPO3 but more of the browsers which are not triggering a onchange event.

So, I can confirm this issue.

A workaround could be to handle onfocus/onblur events (the user was to click/select a field to change data and for saving he will leave this field again).
Another solution could be, to disable auto-fill via <meta> tag like suggested in the article from above. Possibly some browsers already have such feature?

Due to this comes from the browser and TYPO3 could only work around, I'm not sure if this is a major or tweak problem. It could also just be a feature.
But in fact it could annoy/hinder users while administrating data in the TYPO3 back-end.

Hmm...otherwise i think its not least Typo3 which makes itself fully dependend on correctly triggering javascript event-handlers, so i think we should offer a solution even if its just a workaround...? well just my personal opinion.

I would like to emphasise your assumption that this effect could really annoy and hinder users!...and mainly: if you save+close, it may take a possibly fatal while until not saved values get evident...i think its a major issue.

Just a little add note: there exists a non-standard html attribute called "autocomplete" (tested it for Firefox 2 and IE 7 / win and it works) which can be used to switch it off within form field tags...but this is an evil way and actually it would be nice to use the feature instead of disabling it...

The problem most probably is, the naming of the fields.

Firefox recognizes an input-box by its name="" property. In TYPO3 the name-property of each field is different as it has the uid of the field in the name-string. So if you edit an already existing content element, you will get the autocomplete drop-down when editing the same element again.

But for this reason autocomplete does not work with new elements, as they have a random string as uid (NEW0123456789abcdef)

So autocomplete partly works ... you can re-enter an already used value for the same element again.

It would be nice to have this feature for NEW records. The only thing to do would be to generate the NEWxyz string using a repeatable mechanism.