We usually use current versions of Firefox during development. Current versions of Chrome are also tested on a regular basis and usually do not deviate too much from the behaviour on Firefox. Although I have not tested it, current versions of Internet Explorer should also be usable.

Internet Explorer has been the source of many problems in the past. We have managed to fix several IE-related bugs, but cannot make any guarantees what IE7 is concerned, because it is now 6 years old and does not adhere to common web standards (nor did it, ever, to be honest). For a modern and highly interactive web application like Kunagi, this is a huge problem. The other problem is non-availability of such an old browser for testing.

Lastly, the number of visitors on our website using IE7 is now 0.6% and constantly dropping.

I don't want to appear overly intrusive, but have you concidered upgrading your browser? In any case, I don't think support for IE7 and older will improve in the future. On the contrary, it will not only be Kunagi that is not working properly. To name an example, Twitter has announced recently to drop IE7 support for the upcoming versions of their Bootstrap framework. I assume other projects will suffer the same fate.