Remove attempts to invoke integration commands in firefox

[adomasven]

Irrelevant with standalone only. See https://github.com/zotero/zotero-word-for-windows-integration/blob/master/build/template/Zotero.dotm/word/vbaProject.bin/Zotero.bas#L122-L173

Might be able to make Windows Insider versions work https://forums.zotero.org/discussion/69739/zotero-plugin-tries-opening-firefox