There are two security updates released today, but each update belongs to different Slackware version.
The first one is Seamonkey which is now updated to Seamonkey 2.2 and aimed for Slackware 13.37 and -Current only. Older version of Slackware still shipped with previous version of Seamonkey.
The second update was Mozilla Firefox which is upgraded to 3.6.19 and it aimed for Slackware 13.0 and 13.1 only. Firefox on -Current is upgraded to 5.0.1, the latest stable even though it was supposed to be a Mac OS X fixes only.
The only surprise is that Thunderbird 5 is now included in -Current. Only last week Thunderbird gets upgraded on -Current and it was still using the previous 3.x series and 6 six days later, it moves on to Thunderbird 5