v3.8.1 admin not working well

Hello. I just updated to WP 3.8.1 and I’m having some problems with the Admin area, primarily with navigation and CSS. Some areas/pages in admin render OK part of the time, and others don’t at all.

For example, if I go to “Customize”, for a theme, the page will render with CSS from colors.min.css according to Firebug, but that’s it. I can see where load-styles.php?c=1&dir=ltr&load=dashicons,admin-bar,wp-admin,buttons,wp-auth-check&ver=3.8.1 is listed, but the CSS doesn’t render. When I’m in other areas of the Admin I can refresh the page which does sometimes temporarily resolve the issue for that page, so I know the files are intact.

Also, when I hover over a main link, i.e. “Appearance”, the sub-menu doesn’t expand to let me choose anymore. I have to click on “Appearance”, then make a choice once the new page loads. I’ve noticed that sometimes other buttons or links doesn’t work correctly, also. For example, I wanted to edit the name of a brand-new category I created, but it wouldn’t update. I had to delete it completely and make a new one instead.

Some details:
I’ve used WordPress for a long time, so I am comfortable with it, and haven’t had any major issues in the past. This is a localhost site I’m developing before moving it to my web host. I primarily use Firefox, which is up-to-date, but I cross-reference all my work on other browsers as well. I do clear my browser cache, as a check. I have installed an additional test site using 3.8.1 to insure the same issue with a clean install — no added or altered code of any kind.

I’ve tried searching the Forum for information on my exact issue, but nothing I’ve seen has helped.