Comment 2 for bug 179394

Thank you for taking the time to report this bug and helping to make Ubuntu better.
I have you same resolution and firefox version, and I get the same behaviour fo your one.
Anyway, I'm unsure this is really a bug, since it could be an expected beahviour. I'll set the status to incomplete; in the meantime, I suggest you to report this bug on bugzilla (https://bugzilla.mozilla.org/). If you do so, please link the bug here clicking on "Also affects distribution" (left side pane)