Unfortunately you can't turn off the algorithm which treats other people's favourites as if they were retweets, which makes me think twice about using the favourite feature at all. I know I've had stuff put into my feed which the person doing the favouriting would never have retweeted.

I wrote an extension/user script to filter those - and retweets - out into their own lists on the front page [1], as I just want a chronological timeline of what people are saying now, which mustn't be "engaging" enough for Twitter's purposes.

[1] https://github.com/insin/manage-twitter-engagement#readme