Firefox no longer supports the plugin which is coming with the icaclient. However if a proper wfica.desktop file is placed on the system, Firefox will know because of the mime database how to handle the .ica file and launches the icaclient correctly.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=3f6ad4b98dc0ef52285c3373e3b5e844eac3db30 commit 3f6ad4b98dc0ef52285c3373e3b5e844eac3db30 Author: Lars Wendler <polynomial-c@gentoo.org> AuthorDate: 2018-04-01 14:02:37 +0000 Commit: Lars Wendler <polynomial-c@gentoo.org> CommitDate: 2018-04-01 14:13:34 +0000 net-misc/icaclient: Bump to version 13.9.1.6 Added wfica desktop file. Closes: https://github.com/gentoo/gentoo/pull/7695 Closes: https://bugs.gentoo.org/651926 Package-Manager: Portage-2.3.27, Repoman-2.3.9 net-misc/icaclient/Manifest | 2 + net-misc/icaclient/files/wfica.desktop | 12 ++ net-misc/icaclient/icaclient-13.9.1.6.ebuild | 207 +++++++++++++++++++++++++++ 3 files changed, 221 insertions(+)