Its working only in firefox for me
This mean you have browser related issue (not AbanteCart)
That is not correct.
I am a software tester and have been testing software for 17 years. I work in Clinical Trails for medical software, and am regulated by over 20 regulating bodies, just to give you an idea of what I deal with every day. You should never blame the user for the issue until you are very sure. If you want an open source software system to work, jumping to blame the user is not going to win you any customer awards, and without green answering this, I was ready to leave this cart.
I have now tested this on Firefox and all three drop downs work. That is manufacturers, and both category drop downs (Search and category create). It does not work on Chrome with all browser extensions turned off and a brand new install of IE11. You have multiple users reporting this issue, green, mykidz and I. So you have a pattern. Even in browsers, if you have multiple users with the issue and you think it is a browser issue on their machines, it is the products problem, not the users.
When a browser issue happens, users blame the product, they make posts, and other users read those posts, they see it is an issue, it can not be fixed and people do not want to use that product. That is the products problem, not the users. Those users can leave to a new cart. While the browser issue still exists. If the issue is a browser extension, it's AbanteCart carts problem, if its a single browser it is AbanteCart carts problem, if it is a region issue, it is AbanteCart carts problem. The answer should be to find out why it occurs, and how to stop it, 3 people with the brand new hot version are having this problem, that is bad news, it is worse they have publicly posted it and at least on my posts they have been read over 140 times. The answers have been user it is you, not AbanteCart cart we tested it. That is not helpful, and is now proven to be not correct. If you want this cart to survive (I sure do) you should not jump to this conclusion.
Instead of saying it is you user, you ask what they are running, what version, what extensions are installed, you replicate, and then if you don't see and issue, you dig further. You have to find the issue, because if 3 people are having this issue, more people will have this issue, the more that report big issues that make the cart unusable like it was for me, the more people do not install it and others that don't make posts will just leave.
I believe you have an issue with some code and the way that IE and Chrome handle drop downs. I can now use the cart, but I am using it on firefox which I do not like to use. So I am being inconvenienced at a minimum, at least I can report that to other users now that there is a work around, and hopefully AbanteCart cart will reply to that post and say they are looking into the issue for 1.2.1