What are the main differences between Buddhism and Ellen Langer's 'scientific mindfulness'?

For the "big differences", we need to see how Ellen Langer and the Buddha defines "mindfulness" (and "mindlessness" when that helps).

Ellen Langer writes the following:

• "Mindfulness involves two key strategies for improving health: attention to context and attention to variability"

• "The more mindful we are, the more we can create the contexts we are in"

• "The creation of new categories, as we will see throughout this book, is a mindful activity. Mindlessness sets in when we rely too rigidly on categories and distinctions created in the past (masculine/feminine, old/young, success/failure)

• "In the character o Kutuzov, we can find portrayed the key qualities of a mindful state of being: (1) creation of new categories; (2) openness to new information; and (3) awareness of more than one perspective"

• "The more we realize that most of our views of ourselves, of others, and of presumed limits regarding our talents, our health, and our happiness were mindlessly accepted by is at an earlier time in our lives, the more we open up to the realization that these too can change. And all we need to do to begin the process is to be mindful"

• "A very basic and mindless error that we often make is to take the names we give to products/things as the things themselves"

Though she puts a lot of emphasis on categories and being able to work with different perspectives, on the attention to variability she writes:

"When people are depressed they tend to believe they are depressed all the time. Mindful attention to variability shows this is not the case

Finally, I haven't seem her speaking of meditation other than suggesting that it "is a tool to achieve postmeditative mindfulness" -- and it's not clear what meditation technique she is referring to.

Now, what about buddhist "mindfulness" -- sati in pali?

First, it goes without saying that the dhamma is in the context of a soteriology: become permanently free from dukkha (unsatisfactoriness) whereas Langer's is concerned with health.

But I see intersections. Though sati has many different uses, it does have an aspect of awareness and an aspect of memory. Generally, in a gist, it means "to have [something] in mind"; moreover, many of the exercises of sati in the Buddha's teaching are in the form of:

"Breathing in long, he discerns, 'I am breathing in long' [...] "Furthermore, when walking, the monk discerns, 'I am walking.' When standing, he discerns, 'I am standing.' When sitting, he discerns, 'I am sitting.' When lying down, he discerns, 'I am lying down.'

-- Kayagatasati Sutta, MN 19

In other vein, one function of sati is observed both in the Buddha dhamma and in Langer's writings: the recognition of change. However, where Langer advocate the local usefulness of such recognition (e.g. that a depressing state is not permanent) and stops there, in the Buddha dhamma such recognition encompasses these benefits and goes way beyond, aiming to establish by direct experience the impermanence (anicca) of all phenomena we come to contact.

Moreover, Langer's elaboration of categories and perspectives does not have a direct correspondence in the dhamma. It's purpose seem to be, generally, on improving critical thinking -- and there's evidence for that, which is good.

In Langer's mindfulness, the play on categories seems useful to take one out of an illusory context. However, a Buddhist would continue that sentence saying: "...by putting one in another illusory context/category". That is, buddhists are taught to have "direct experience", insight -- without intermediary categories interfering -- by learning to observe the entire mind process, from bare experience to understanding how mental formations come into play -- assisted by buddhist psychology (five aggregates, six senses) and buddhist soteriological context (eg. three marks of existence: unsatisfactoriness, impermanence, not-self). This emphasis on detailed observation of the mind and the minutia of mind processes fully encompasses Langer's notion by going much deeper in the problem of illusory concepts -- making Langer's mindfulness seem gross in comparison to my eyes.

Finally, for an in depth treatment of minfulness in early buddhism, I suggest the book Mindfulness in Early Buddhism by Tse-Fu Kuan.