I had actually been having trouble lately. Clicking links in email no longer launched anything. On my laptop, Sleipnir would launch even though Firefox was set as the default browser…
The cause was Sleipnir.
Under “Tools > Sleipnir Options” in Sleipnir, there is an item labeled “Set as the default browser.” Once you click it, Sleipnir remains the default browser even if another browser believes it has made itself the default. Worse still, this setting remains effective even after Sleipnir is uninstalled. In that case, there is no browser to launch, so clicking a link launches nothing.
I had been troubled by this for about 2 months, but today a colleague, N, pointed out that there seemed to be a bug somewhere around there. I reinstalled Sleipnir and changed the setting, and it was fixed.
But wow…