Valve have announced a new Steam client update has been made available with a big list of fixes that include the likes of:

• Made connections to misbehaving content servers timeout and retry a new server correctly
• Workaround for a Firefox 3.5 bug where they activate random windows after minimizing which would confuse the state of some Steam windows
• Fixed overlay bug where opening the overlay from an in-game menu (ie, Invite Friends in a L4D lobby) could result in the overlay opening and closing immediately if you had previously used the "Close" button in the overlay itself

Among much, much more. To grab the update click the file menu inside steam and find "Check for Steam Client Updates...". The full list of fixes can be found here.