XP Pro Sp3. Firefox 23.0.1. Thunderbird 2.0.0.25pre (by choice!). NAV 2012 (19.9.1.14) by choice.
Click-links embedded in Thunderbird 2.0.0.25 emails won't open in Firefox 23.0.1 .. whereas Firefox opens okay from links in Outlook Express. If I change the default browser to IE8, no problem to open IE8 from click-links in Thunderbird 2.0.0.25. And, no problem to open Firefox from links saved to the Desktop, etc., etc.
Problem is the same on three different computers, all running the same OS and the same versions of Thunderbird and Firefox as mentioned above. All three have Thunderbird 2.0.0.25 installed since 2010 and I haven't had a problem click-starting (in Tb) the different Fx versions as they became available .. until a few weeks ago (and around the release of 23.0/23.0.1).
Solution (work-around): It seems the NVP 12.0.0.380-1 Firefox extension is the culprit, as, once disabled, the click-link problem went away. So far, I have checked on two computers and it's gone once NVP is disabled. Time-frame-wise, this would tally too, as the current version of NVP was (I think) introduced about the time I started to have these issues.
Any suggestions? Thanks.