Of course it is. In most cases you do not have any sort of guarantees regarding the browser (which it self usually is more complex piece of software than all your operating system and it's accessories calculated together - difficult to audit - known to collect metrics etc etc). In addition one can sandbox their local terminal pretty effectively - With Tomoyo or some other MAC technology. It's not so bad idea to actually isolate your browser too (with Mandatory Access Control) - It usually has no business for a global view on your filesystem or local network resources.