how you determined that Jehovah's Witnesses are wrong

Nothing the Jehovah's Witnesses said would happen did in the time frame they have given and repeatedly altered.

I have been a Jehovah's Witness and I wonder how you determined that Jehovah's Witnesses are wrong and that Mormonism is less wrong or even right?

As to how I came to believe in Mormonism, see above. As to why I think JW are wrong, one of my strongest religion-related beliefs is that the Book of Mormon is what is says it is, an ancient record. I find no other explanation plausible. (More on this below). That rules out JW and other religions’ exclusive truth claims, though I find many religious practices good and believe many other religions have part of the truth.

Is Mormonism falsifiable?

Yes, throw out the Book of Mormon and the rest tumbles down.

What probability do you assign to Mormonism being wrong?

I find only one alternative remotely plausible, namely that there is no God and what I interpret as spiritual experiences are actually delusions. But other than testing against measurable reality, which I’m already trying to do, it’s difficult to judge the probability that you are delusional. Perhaps anywhere from 5 to 20%.

How do you feel about Isaiah 13:15-18?

The standard Mormon view is that the Bible is imperfect because people edited it and added and deleted and changed stuff and history follows a pattern of God choosing a prophet and people deciding to disobey that prophet and living in spiritual darkness. When they are ready, God will choose another prophet, etc.

I believe both of those. I also believe that, given the existence of passages like the above, a lot of people writing the Old Testament were the same people who were living in spiritual darkness.

If I may:

1. JohnH went ahead and gave an excellent answer; I'll not reiterate.
2. Yes; the problem is that archaeology is slow. :P However, there have been many findings that have actually confirmed Mormon claims; these are usually then ignored by those same people who used them as their strongest points. (cf. writing on golden plates, use of cement in ancient America)
3. About 30%.
4. I fail to see the problem with this scripture, though we in our church hold the KJV to be a better (not by any means perfect) translation of the Bible. Are you saying that it doesn't sound like something a "loving God" would do? God uses the designs of evil to suit his purposes, which are, in the long run, good. The ur-example is Satan's temptation of Adam and Eve, without which mankind (well, two of them anyway!) would be stuck in stagnation, and the rest of us would be stuck in heaven, waiting for the two of them to get on with it.

I have been a Jehovah's Witness

Hey, me too!