After recend update to Firefox 38.0.1 my menu's and fonts are HUGE

I applied an update today (June 1 2015) and firefox now displays with fonts so large that the top 1/3 of my screen is consumed by the menu, tabs and bookmarks area. Its utterly useless this way. Reducing the fonts only changes the web page size and leaves the rest of the browser looking ridiculous.

Anyone else observer this?

Are you perchance using the Ubudao icon set? In the past I have experienced something similar with Audacious which is also a Gtk2 application.
Try changing your icons to Oxygen for ex: logout log back in and see if that clears the problem.

That’s the only thing I can suggest.

Perhaps your zoom got jiggered?

Click on the settings icon(3 horizontal bars on the button top right), second row from top should read

  • 100% +

If not, click on the minus button until it reads 100%.