Problem in firefox browser, how to solve?

Question

Mozilla Firefox

On the site toster.ru , I have an incomprehensible problem - when entering text into an input or textarea, strange things happen: when I type any text, keystrokes do not always "work" i.e. I write for example "mom", but only "maa" or "ma" will turn out; also when deleting errors, after pressing the Backspace key, either nothing happens, or 2 characters are deleted at once.
There is a similar bug (?) periodically, I don’t know what caused it. Using Firefox 41.0 , other sites have never experienced anything like this and while restarting the browser helps, the residue remains.
I can’t say for sure that the problem is on the part of the Toaster, but I want them to pay attention to it.

Answer 1

Maybe a problem with the keyboard?

Answer 2

I met this with friends both in chrome and in the opera. Reinstalling Windows helped. my friends don’t keep a close eye on cleanliness, I suspect that this is some kind of crooked keylogger working) draw your own conclusions from this)
I had this for a very long time and was connected with an old computer that could not keep up with my tapping on the clave, but I think this is not the case