No, don't buy Suitcase. Get the free Linotype FontExplorer:
http://www.linotype.com/fontexplorer.
Then deactivate all fonts in FontBook (apple's font program) and shut it down for good.
Use FontExplorer to Tools/Manage System Font Files and move all your non system fonts out of system/fonts library/fonts. All your user fonts should be in a folder inside your hard drive, not in any system folders.
Should work. Also, make sure Helvetica isn't your default font in your browser. Use Tahoma, Verdana, or Georgia. Maybe Arial.