I, always, consider that a new version is a final version, and the a and bs are preliminary and possibly unstable/ troublesome/whatever. It seems that for the Mozilla types, a new version is, anything, with a higher number, be it alpha(probably) or beta(definitely. I had gravitated toward Seamonkey, because, I thought that it was staying with the old ways, but I was mistaken.
Last night, Seamonkey gave me a noticed that there was a new version, SM 2.3, and, instantly closed the attempt to download. This morning, Seamonkey started with the tell-tale bar indicating that an update was being installed. Everything appeared to be in order, all addons seemed compatible until, I tried to delete one e-mail message. Instead of disappearing, it opened a page which showed multiple copies of the toolbar icons, and no text.
I closed that mess, and tried to open a message, and it looked like that delete attempt. This went on with several accounts. I closed Seamonkey, and deleted the .msf files, to no avail. This alleged SM2.3 was a mess, and the UA showed it was based on rv.6.0. However it was still a b1.
I checked my Preferences, and saw that Advanced|Software Installations was set to download and install the update. I don't want surprises, but I missed that setting. This is doubly galling. To get an update, and not knowing that it was going to be installed, but also a beta, which was a mess!
To make a long story short, I download v.2.2, and installed it, on top of this pseudo 2.3, and all is well.
And, yes, I did uncheck the automatic installation. So, beware!
UserAgent: Mozilla/5.0 (Windows NT 5.1; rv:5.0) Gecko/20110706 Firefox/5.0 SeaMonkey/2.2