hi, first I'd like to tell you that I'm not a js developer I just need a little help, hope it won't be too complicated to understand for me

I need to click by code on a button which has no 'ID', 'name' nor 'tag. It has only 'class' and 'tab index'.
After some googling I found that there is possible to use GetElementbyClassName (which should work on firefox) but I;ve not been able to make it work. Could anybody give me an example of code which can handle this task?

thank you