fixed l10n broken display texts an buttons on theme page (bug 920002)

This fixes https://bugzilla.mozilla.org/show_bug.cgi?id=920002 (page before the fix: https://addons.mozilla.org/de/firefox/themes/)
![css_themepage_l10n-920002](https://f.cloud.github.com/assets/145172/1211241/7d2f56dc-2606-11e3-9ac6-f93c53854231.png)