The more I work in Umbraco the more I am slowed by having to have one file open at at time. 

Compare umbraco to Visual Studio in this regard. (I know they are chalk and cheese but hear me out)

In VS I might be working on serveral files at once. All of them are open in tabs accoss the top of the screen. 

In Umbraco I might be working on some XSLT, a template or 2, some css a couple of js files and what ever else. Some in the Settings tab, others in the Developer tab all in differnt folders. What a mess.  

What would be nice is if you could have a 'save and keep open' button at the top of each page. Hitting that adds a url to some tab list that appears at the top of the Umbraco desktop so you can easily jump to each item. 

Here is a mockup of how that might look. 

I'm pretty sure Umbraco does not do this now, but boy would it be a handy feature to add to future version. 

(Edit: Tweaked the mockup image)