Also, try Phony with Fennec, which lets you pose as using variuos pre-configured browsers, including desktop firefox, iphone and android. That might help?
Hide UA, without customisation, prevents use of Ovi - probably just needs extending to have a selection of UA strings. On the other hand I seem to remember HUA could be customised to anything so it might be able to pose as any, including a symbian browser.
Sorry to say, no idea what the symbian UA string is but shouldn't be that hard to find.