Here is my problem, which is similar to you, and my solution, which is mainly about fixing the CSS files’ mime type in the Windows. I hope it will help you!
The help browser display is unformatted, i.e. no CSS style sheet file is loaded when rendering the local web page of help document.
System Environment: Windows 8 64bit; MATLAB 2014a; IE 10 (the original version come with Win8)
First, I found this bug report with a solution of applying a patch. http://www.mathworks.com/support/bugreports/989850 I noticed its aim is IE 11, which is not my case. But I still tried it, it didn’t work. I found that solution is about a localnav.js, it just adds some special treatment towards IE11.
I pressed F12 in IE to get into the Developer Mode and found the console error output: CSS was ignored due to mime type mismatch I came to know that it is the mime type ’s new restriction in IE 10+ that caused this error.
Then I googled the error and found this web page
And I just used the utility called FileTypesMan from NirSoft to have a look at my local OS's mime type setting for .css file. That utility saved my effort in find that in the Microsoft Registry Editor (regedit.exe).
It did help! I found the wrong mime type.
I found my Microsoft Expression Web (which is the successor of FrontPage) have changed the mime type when I installed it. Because I usually use chrome to open the local web page, I never notice that change.
After change it back to text/css, there is no error at all. And both in IE and MATLAB’s Help Browser, the help document is displayed correctly.
Hope that changing the local setting of .css file's mime type can help you too!