Same here. Current Mountain Lion 10.8.2, Firefox 18.0 Retina on macbook pro retina, second monitor is LED Cinema Display. Firefox window NOT in fullscreen (and smaller than retina full screen)

With firefox on main laptop screen, extras like suggestions from typing in URL-box appear in correct location, correct scaling. Drag firefox to 2nd monitor, firefox operations appear OK EXCEPT for said prompts.. which appear on main retina screen at some arbitrary location but 1/2-size (i.e. point sizes are for non-retina)

Dragging firefox back to main screen, back to normal good functionality.

Try to disable hardware acceleration in Firefox.

• Firefox > Preferences > Advanced > General > Browsing: "Use hardware acceleration when available"
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• https://support.mozilla.org/kb/Safe+Mode

You can also check for problems with the localstore.rdf file.

• http://kb.mozillazine.org/Corrupt_localstore.rdf

Tried turning off hardware acceleration as recommended. No improvement. Leaving it turned off, and restarting firefox in safe mode, no improvement.

I have been using this config of monitors with previous Firefox 16, 17 etc.. just goes wrong since 18.0

Disabling Hardware Acceleration made no difference.

(

Other ideas?

There are issues with retina (HiDPI) support that will be fixed in an upcoming Firefox 18.0.1 version, so keep an eye on that.

I just got 18.0.1 - It fixed the issue.