New stocks symbols can be entered several at a time in the text field on the toolbar. You can find ticker symbols by going to "http://quote.yahoo.com/l?o=t" (US and Canada) or to "http://quote.yahoo.co.uk/lookup.html" (UK, France, Germany).
The QuoteGrabber might not recognize what stock exchange a symbol belongs to and thus won't know what server to contact to get quote data. For any non-US stock symbol you should append a two-letter country extension to the symbol when entering it. These country extensions are the same as Internet extensions: "fr" for France, "uk" for the UK, "de" for Germany.
For example "British Airways" has the symbol "BAY" on the London stock exchange, so enter BAY.UK (or bay.uk, case is not important). The German stock "BASF" has the symbol "515100", so enter "515100.de". Paris stock "Air Liquide" has the symbol "12007", so enter "12007.FR". If you enter a symbol without extension it will be considered as a US symbol, in any case you can always add ".us" to your tickers. Canadian stocks already have an extension (.M, .TO, .VC) depending in what Canadian market they are traded, and this extension will be recognized as Canadian.