Firefox 4 - blink and its gone!

[#1]

I know some of you may think it foolish, but I tend to trust software I've used for sometime update itself. Yesterday morning I received a "security update" from Firefox and allowed it to install. I bit later I noticed that the green button for my Trusteer Rapport software had disappeared from toolbar - the software was still running but not checking anything. Going to the Trusteer website I see that Firefox 5 was only going to be supported by the end of this month - but I thought I still had Firefox 4. NO! The security update was in fact an update to Firefox 5 (see below).
Anyone know why there has been such a rapid version change and why it was called a security update?

[#2]

Talked about here...http://community.plus.net/forum/index.php/topic,96522.msg815896.html#msg815896
Explanation here...http://blog.mozilla.com/blog/2011/06/21/mozilla-delivers-new-version-of-firefox-first-web-browser-to-support-do-not-track-on-multiple-platforms/

[#3]

But basically Mozilla have just move the decimal point so instead of going from Firefox 4.0 to 4.1 they have gone from 4 to 5.!

[#4]

It means that Trusteer report needs an upgrade to work - Kaspersky has the same problem (note I disabled Firebug as I don't use it normally)
It will sort itself out eventually when a new version is released

[#5]

Quote from: ReedRichards

But basically Mozilla have just move the decimal point so instead of going from Firefox 4.0 to 4.1 they have gone from 4 to 5.!

I know, Crafty isn't  It, I reckon they were all out of cake and needed more

[#6]

Thanks for the pointers to further info.
I read elsewhere that this is a new tactic by Firefox too rapidly reach a version number higher than 9 - for some reason

[#7]

Update.
New Trusteer software now available - downloaded, installed and I now have my green button back on the toolbar of FF5