I found these settings eventually.
They are stored in an XML file called browsers.xml in thge following directory:
**C:\Documents and Settings\%USERNAME%\Local Settings\Application Data\Microsoft\Visual Studio\9.0**
The XML should look like this:
<?xml version="1.0"?>
<BrowserInfo>
<Browser>
<Name>Firefox</Name>
<Path>"C:\Program Files\Mozilla Firefox\firefox.exe"</Path>
<Resolution>0</Resolution>
<IsDefault>True</IsDefault>
<DDE>
<Service>FIREFOX</Service>
<TopicOpenURL>WWW_OpenURL</TopicOpenURL>
<ItemOpenURL>%s,,0xffffffff,3,,,</ItemOpenURL>
<TopicActivate>WWW_Activate</TopicActivate>
<ItemActivate>0xffffffff</ItemActivate>
</DDE>
</Browser>
<Browser>
<Name>Internet Explorer</Name>
<Path>"C:\Program Files\Internet Explorer\IEXPLORE.EXE"</Path>
<Resolution>0</Resolution>
<IsDefault>False</IsDefault>
<DDE>
<Service>IExplore</Service>
<TopicOpenURL>WWW_OpenURL</TopicOpenURL>
<ItemOpenURL>"%s",,0xffffffff,3,,,,</ItemOpenURL>
<TopicActivate>WWW_Activate</TopicActivate>
<ItemActivate>0xffffffff,0</ItemActivate>
</DDE>
</Browser>
<InternalBrowser>
<Resolution>0</Resolution>
<IsDefault>False</IsDefault>
</InternalBrowser>
</BrowserInfo>
The <IsDefault>
tag determines whether or not the browser is used for debugging.