Although I don't see something obviously wrong in the browser I see an error in the console: Error: uncaught exception: [Exception... "Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIPrefBranch2.addObserver]" nsresult: "0x80070057 (NS_ERROR_ILLEGAL_VALUE)" location: "JS frame :: chrome://global/content/bindings/tabbrowser.xml :: :: line 2274" data: no] Source File: chrome://global/content/bindings/tabbrowser.xml Line: 142 Happened for the first time between 1.9a1_2006060208 and 1.9a1_2006060212. http://bonsai.mozilla.org/cvsquery.cgi?module=PhoenixTinderbox&date=explicit&mindate=2006-06-02+07%3A00&maxdate=2006-06-02+13%3A00

Also another error shows sometimes up: Error: gPrefService.savePrefFile is not a function Source File: chrome://browser/content/browser.js Line: 1056

I see the first error also in branch, but not the second error. The second error has the same regression range. It shows up together with the first one, or not at all.

Yeah... this is my fault.

if we fail to register the observer, the observe method won't be called, so we should also see a regression where changes to the browser.tabs.disableBackgroundClose pref are not heeded (until you open a new browser window) but using LXR i don't see any UI for settting that pref, so it must be a hidden / developer, so you'd have to use about:config to verify the regression. (adam, I'm interested because of bug #318168)

*** Bug 340998 has been marked as a duplicate of this bug. ***

adam (ispiked) and I have been discussing this on IRC, and I have a patch. the patch is based on something that dave townsend (mossop) linked to adam, see http://svn.blueprintit.co.uk/viewvc/mozilla/firefox/TabSidebar/trunk/src/chrome/global/content/widgets/previewevents.inc.xml?view=markup#l_13 I'll attach our fix (for trunk, but this error is on both branch and trunk.)

Comment on attachment 225075 [details] [diff] [review] patch seeking mconnor's review, since he knows about bug #339477

fix checked into trunk and branch. thanks again to adam (ispiked) and dave (mossop) for the help.