Dear Andreas, The zotero changelog,
https://www.zotero.org/support/4.0_changelog ,---- | Changes in 4.0.26 (February 11, 2015) | Functionality added or changed | Firefox 36 compatibility `---- indicates that zotero <4.0.26 has compatibility issues with Firefox 36. Giving a try to Firefox 31 from jessie or zotero-4.0.26 from sid might be a good idea. Cheers, Benda
