I have high confidence this is the issue. - https://searchfox.org/comm-esr128/rev/38abeb35c357a3032d84535d7c26da4ea37c4605/mail/base/content/messenger.js#174 calls specialTabs.openSpecialTabsOnStartup() - https://searchfox.org/comm-esr128/rev/38abeb35c357a3032d84535d7c26da4ea37c4605/mail/base/content/specialTabs.js#740 calls this.showWhatsNewPage(); - https://searchfox.org/comm-esr128/rev/38abeb35c357a3032d84535d7c26da4ea37c4605/mail/base/content/specialTabs.js#1040-1046 is the fun... the override_url pref is the fallback default, usually empty. in `getPostUpdateOverridePage` it can be overridden by a "showURL" action in the XML returned by Balrog. That looks like this: (as of last night, abbreviated for clarity) <update xmlns="http://www.mozilla.org/2005/app-update " appVersion="128.0" buildID="20240709010607" channel="esr-localtest-next" detailsURL="https://live.thunderbird.net/thunderbird/releasenotes?locale=en-US&version=128.0&channel=esr" displayVersion="128.0esr" installDate="1720561567742" isCompleteUpdate "true" name="Thunderbird 128.0esr" previousAppVersion="115.12.0" promptWaitTime="86400" serviceURL="https://aus5.mozilla.org/update/6/Thunderbird/115.12.0/20240610193835/Linux_x86_64-gcc3/en-US/esr-localtest-next/Linux/default/default/default/update.xml?force=1" type="minor" statusText="The Update was successfully installed" actions="showURL" openURL="https://live.thunderbird.net/thunderbird/whatsnew?locale=en-US&version=128.0&channel=esr&oldversion=%OLD_VERSION%" foregroundDownload="true"> Assuming there's no "silent" in the update XML and the enterprise policy is not blocking it, the openURL property has the what's new page URL which is passed to openLinkExternally. (Side note, the "detailsURL" field is where the release notes URL comes from that is populated into the about: dialog and a few other places.) Testing this scenario is a bit of a pain outside of a release context. There is `toolkit/mozapps/update/tests/browser/browser_showWhatsNewPageTest.js` which could probably be adapted for Thunderbird.
Bug 1906983 Comment 6 Edit History
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I have high confidence this is the issue. - https://searchfox.org/comm-esr128/rev/38abeb35c357a3032d84535d7c26da4ea37c4605/mail/base/content/messenger.js#174 calls specialTabs.openSpecialTabsOnStartup() - https://searchfox.org/comm-esr128/rev/38abeb35c357a3032d84535d7c26da4ea37c4605/mail/base/content/specialTabs.js#740 calls this.showWhatsNewPage(); - https://searchfox.org/comm-esr128/rev/38abeb35c357a3032d84535d7c26da4ea37c4605/mail/base/content/specialTabs.js#1040-1046 is the fun... the override_url pref is the fallback default, usually empty. in `getPostUpdateOverridePage` it can be overridden by a "showURL" action in the XML returned by Balrog. That looks like this: (as of last night, abbreviated for clarity) <?xml version="1.0"?><updates xmlns="http://www.mozilla.org/2005/app-update"><update xmlns="http://www.mozilla.org/2005/app-update" appVersion="115.12.2" buildID="20240621154414" channel="esr" detailsURL="https://live.thunderbird.net/thunderbird/releasenotes?locale=en-US&version=115.12.2&channel=esr" displayVersion="115.12.2" installDate="1720622824411" isCompleteUpdate="true" name="Thunderbird 115.12.2" previousAppVersion="115.12.0" promptWaitTime="86400" serviceURL="https://aus5.mozilla.org/update/6/Thunderbird/115.12.0/20240610193835/Linux_x86_64-gcc3/en-US/esr/Linux%206.9.8-zen1-1-zen%20(GTK%203.24.42%2Clibpulse%2017.0.0)/ISET:SSE4_2,MEM:128585/default/default/update.xml" type="minor" statusText="The Update was successfully installed"><patch size="62676836" type="complete" URL="https://download.mozilla.org/?product=thunderbird-115.12.2-complete&os=linux64&lang=en-US" finalURL="https://download-installer.cdn.mozilla.net/pub/thunderbird/releases/115.12.2/update/linux-x86_64/en-US/thunderbird-115.12.2.complete.mar" selected="true" state="succeeded" hashFunction="sha512" hashValue="03eabd9b8b106f289dcd4439f2c4d7b289211d61f67af2fb80edbf1f282000e21c8fc47de8b13b168a9729fd21d6f009abb346db77e6618638d5157af70dd531" internalResult="0"/></update></updates> Assuming there's no "silent" in the update XML and the enterprise policy is not blocking it, the openURL property has the what's new page URL which is passed to openLinkExternally. (Side note, the "detailsURL" field is where the release notes URL comes from that is populated into the about: dialog and a few other places.) Testing this scenario is a bit of a pain outside of a release context. There is `toolkit/mozapps/update/tests/browser/browser_showWhatsNewPageTest.js` which could probably be adapted for Thunderbird.