Thats the most negative part of opera that some sites do not open
Microsoft's Internet Explorer has itss own core based program
whereas opera and firefox have independant program core
so some sites which are totaly based on IE core cannot be opened in any other browser which is not IE based
but the browasers like maxthon,green browser,deepnet,etc
are IE core based and therefore can open all the sites with the sites totally based on IE core
hope its enough for you
also for gmail only we have to go for IE
but opera 9 may include both the cores in which instant switching may be possible so we would not run for other browser
For Firefox it is in its testing stage so it cannot open more sites
coz its new and u now old is gold
i.e IE and lately Opera are the best browsers on the planet
IE sucks !