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This is one of the hands that I encountered today in Tenhou:

(Aka) (sorry I don't know how to upload a pic)

I'm North with the hand as shown above in the last round of a tonpuusen with aka and open tanyao allowed. I tsumo 9m and won the hand. I realized later that I was waiting for 69m and 25s (at the time I only saw 69m and 2s ); however, since I already discarded 9m at the very beginning, am I considered in furiten in this situation? If someone had thrown 69m or 25s, could I have won? I don't recall seeing the furiten words at the bottom of the screen when I riichi'ed. I thought I understand the furiten rule pretty well, but I'm quite confused now. Anything clarification will be greatly appreciated. Thanks!

If you did discard the 9m earlier, you were indeed furiten, you couldn't have ronned! Don't know if tenhou would have prevented you to or would have let you proceed and pay a chombo, though, I'm not familiar enough.

For a quick review, you are furiten if :
-you discarded one of your outs earlier
-someone else discarded one of your outs since your last discard and you didn't take the win
-someone else discarded one of your outs since you declared riichi and you didn't take the win.

And as you stated, you couldn't have won on any of your outs if they were discarded, you are not furiten on the 9m, you are furiten and that's all.

Tenhou should tell you about your furiten status *after* your discard once in tenpai. When not tenpai, it won't tell you that you burnt a wait. It might propose that you can chii or pon a tile but it will not propose an illegal win.

As Gnom said, waits aren't furiten: the hand is. If one wait is burnt, they all are.

Thanks Gnom and Senechal! So I was super lucky then, got an ippatsu for the hand as well ! Seems like there's still plenty for me to improve on in tile efficiency. Sigh! I know the rule is the rule, but I still feel it's a bit unfair to be forbidden to ron on 25s which is quite unrelated to 69m. Hehe. Anyway, thanks again guys!

Being furiten in itself is not necessarily a bad thing, the question is to know if it improves the odds that you win (or more precisely the gain in points times the odds of winning —is it called "hope" in English as it is called "espérance" in French?) In this cas you had 4 outs but many of them where in your hand, so you were a bit lucky, but declaring riichi when furiten if you have a decent chance of picking up one of your out allows you to get one more yakus (and potentially additionals hans from tsumo/ippatsu and ura doras depending on the rules and the luck), and depending on the situation it might pressure your opponents enough that they'll fold, giving you more time to pick up your tile. So if the wait is good, declaring riichi while in furiten may be superior to damaten depending on the situation.

The french term "espérance (de gains)" translates to "expected value" in English. Poker players use it all the time to comment plays as being +EV, or -EV.

Having a 3-way, 4-way or more complex wait with sufficient outs, while partially restricted by furiten, remains +EV. I'd usually draw the line at 6 active tiles remaining, where calling riichi while furiten is acceptable. Of course, having a potential wait with a big payoff (ryanmen for sanshoku) has an effect on the evaluation of the hand's potential.

Sigh! I know the rule is the rule, but I still feel it's a bit unfair to be forbidden to ron on 25s which is quite unrelated to 69m.

if you think that seems unfair, remember,
Furiten (temporary or not) is for missing an opportunity to complete the hand, not just to win it.
Even letting pass a tile for a non-winnable hand will get you furiten.
I fell into that trap a few times when I started out. Not anymore.
viewtopic.php?f=5&t=51553&start=15#p57101

Thank you all for your insights!