You actually trust the browser less than the individual apps developed by different companies? I'd think the apps would have more security holes than a browser that's been tested and used by millions of people everyday.
Yeah, in general. Twitter has had XSS flaws that hit people using web browsers but I've not heared of any Twitter app exploits. I'd trust Thunderbird+IMAP more than Firefox+GMail without a doubt. I don't read my RSS feeds in a browser either, they get pulled down and converted to emails and are read in Thunderbird.