One slight inconsistency here is that the version number shown for add-ons is the new version, whereas the version number shown for userscripts is the currently installed version. See this screenshot:
The YouTube userscript is being updated from 1.3.5 to 1.3.6, but shows the current version (1.3.5), whereas the add-ons that are being updated show the version they'll be updated to. For example, here Adblock Plus is being updated from 2.0.2 to 2.0.3.
I'll need to confirm but the behavior I remember is:
This is just how Firefox works. Find a restartless extension, install an old version, turn off the "Update add-ons automatically" option, and manually check for updates. You'll then see the available updates tab, and it will behave this exact way.
This in Mozilla/5.0 (X11; Linux i686 on x86_64; rv:11.0) Gecko/20100101 Firefox/11.0. This is the default behavior. If I repeat this, but after step 4 I open the detail page for this extension and turn Automatic Updates to Off, only then does the 'available updates' tab appear. And I can confirm that the new version (the one that would be installed by the update, not the installed version) is indeed what appears here. I can't reproduce the bit for user scripts because at the moment, there is no "available updates" feature (in #1053 found updates became installed automatically). So this should happen as part of #1455, which would bring it back.
Mozilla/5.0 (X11; Linux i686 on x86_64; rv:11.0) Gecko/20100101 Firefox/11.0
As correctly pointed out on the -dev list ( https://groups.google.com/d/topic/greasemonkey-dev/2cp4VLDSjWo/discussion ) now that update handling is "fixed" to be internally consistent (as of 1.4) this bug exists again and is fixable.
Remove a bunch of old manual-update support code.
Instead make "availableUpdate" the parsed script when it was determined to be a valid update. (To support coming fix for #1497.)
Display the new update's version in 'Available Updates'.
Name and description, also.
Fix downloading updates from the right URL.
Refs #1497 - Introduced bug