I also prefer FireFox and Thunderbird as a internet explorer and email client because it's easier to sync with your Android phones than other applications.
I found this nice plugin for FireFox called "Telify". Telify recognizes phone numbers on web pages and in email messages and converts them to clickable links.
OpenCats is a webapplication and as aspected the plug-in works as it should.
I'm using it with the 3CX softphone.
Just one klick and the phone starts calling.
It's not necessary, just easy .... a so called: "nice to have"
For those don't know: their is a skype module for OpenCats.
You find it in the directory ..../doc/examples/skype.tar