Just updated to new FireFox 29 and I noticed an Issue when editing the Your Communities section. The "Add"-Button is placed on a new line below the TextBox.
Other Browser like Chrome and IE have no issues. Zoom-Level is set to 100%.

The "Add" button is now properly aligned in the Firefox browser.
I have verified the alignment issue in the Firefox 50.1.0.
The recent screenshot in Firefox for your reference:
43.0.3