I see that you are using a MS server?

Did you check that server for server side (ASP) scripts that might be causing that problem?

It seems to be working better if the AskTbASK/3.8.0.12304 part is positioned after the Firefox part.

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.8) Gecko/20100722 Firefox/3.6.8  AskTbASK/3.8.0.12304  (.NET CLR 3.5.30729)

That would suggest a too sensitive check for the "Gecko/20100722 Firefox/3.6.8" part of the user agent.

ASP.NET has a Request.Browser Property which when given the above user-agent string with ASK tb keys gets confused and says its Mozilla 1.0. (in case normal case, it would call it Firefox 3.0). Due to this a related browser specific css file was not linked.

Note: the issue occurs only with .NET 2.0 (till 3.5, becoz 2.0 is the base framework). They use .browsers file in Framework\[versionNumber]\Config\Browsers folder to identify a browser. This mechanism is enhanced in .NET 4.0 and so the issue does not exist in 4.0.

Thanks for a timely reply.

You're welcome.

Identifying a browser via the user agent is very tricky.
You may need to test it as well with coming Firefox 4.0 user agents that are simplified by removing a lot of privacy sensitive information:

Mozilla/5.0 (Windows NT 5.1; rv:2.0b6pre) Gecko/20100909 Firefox/4.0b6pre
Mozilla/5.0 (X11; Linux i686; rv:2.0b6pre) Gecko/20100909 Firefox/4.0b6pre