In order to have the fast speed of website, the web sever compress (gzip) the html files before sending to our clients. When running selenium tests, it shows a pop-up saying: You have chosen to open ... which is a: Bin file from: http://... Would you like to save this file? "Cancel" "Save File"
It seems that the compressed html file doesn't unzip and browsers recognise it as Binary file.
I'm not sure why Selenium does this, because it doesn't seem to happen in all cases (in one case, a server that serves up gzip doesn't give selenium problems, but another server does).
However, after some research, I found a somewhat simple solution. Create a custom Firefox profile for selenium to use (you will have to specify the directory via the command line). Then, load up that profile and goto about:config and set "Network.http.accept-encoding" to "". Now firefox will not send out the accept-encoding header, and if your server is configured properly, it will not send back gzipped content in response. Then, your observed error should not occur any more.