Hi.
Sometimes i want to click RMB and view HTML source, but menu disabled in Firefox. And i switch to the Internet Explorer browser again for it...

Any ideas?

It's known behaviour. FF does not support "view source" in terms of API where we could get source in text form. It can only open ANOTHER window with PRE-FORMATTED text if corresponding protocol scheme is used. See http://en.wikipedia.org/wiki/View-source_URI_scheme for further details.