Firefox takes too long to open all browser tabs in load test tool

[atsakiridis]

Reason is that I'm using a logic to open one by one all needed browser tabs and for some reason Firefox seems to not handle that very well in some environments (namely in OSX where I'm trying to open 50 tabs and I end up with one). The way I had found to workaround this is to open one tab per sec and the issue no longer occurs.

The problem is that this scales pretty badly and the user has to way a long time for the test to start. So instead of that let's open all tabs in a single firefox (and chrome) invocation