User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0 Build ID: 20180628175621 Steps to reproduce: Updated from an older version to the current version 52.9.0 Actual results: After restarting Thunderbird, I was asked to compress offline folders. The popup windows said, this would save "22612 GB" hard drive space. However, the size of my hard drive is 500 GB. Expected results: The correct amount of space to be saved should be displayed.

thanks for filing the bug report. That's quite interesting. If you had to estimate/guess, would 22612 MB be accurate savings? A starting point might be, how big is your Thunderbird profile directory?)

Markus, you are on linux with a German locale? Do you get faultly compact values?

Note the bad German "freigeben" when it should be "freigegeben: :-( https://dxr.mozilla.org/l10n-central/rev/440235f6e07766c98ea936bf31654d6565d9388d/de/mail/chrome/messenger/messenger.properties#76 The amount of space it calculated in code here: https://dxr.mozilla.org/comm-central/rev/6731dac68a6610d4e81447580c225ba8d63cbc97/mailnews/base/util/nsMsgDBFolder.cpp#1938 FormatFileSize() here: https://dxr.mozilla.org/comm-central/rev/6731dac68a6610d4e81447580c225ba8d63cbc97/mailnews/base/util/nsMsgUtils.cpp#485 uses various abbreviations from messenger.properties which are this in English: byteAbbreviation2=%.*f bytes kiloByteAbbreviation2=%.*f KB megaByteAbbreviation2=%.*f MB gigaByteAbbreviation2=%.*f GB The German translation at https://dxr.mozilla.org/l10n-central/rev/440235f6e07766c98ea936bf31654d6565d9388d/de/mail/chrome/messenger/messenger.properties#497 is correct. So this doesn't appear to be a localisation issue.

Right now, Windows says my profile folder is 12.4 GB. But please note that I did click on the button to compact the folders after this popup was presented! Is there any way to make this popup appear again? Further information - don't know if that helps: I use IMAP exclusively and I have lots of accounts. Some of them are really big. The advanced settings are configured to automatically compact folders bigger than 20 MB (just like on the screenshot over here: https://support.mozilla.org/en-US/kb/compacting-folders ). As far as I can tell, I was never asked to compact folders before, and I also think that I did never compact any folders. But unfortunately, I am not 100% sure about that. I installed Thunderbird on this machine in 2014.

version 52.9.0 fixed an issue where for several years imap folders were highly likely to be automatically compacted. See release notes https://www.thunderbird.net/en-US/thunderbird/52.9.0/releasenotes/ which are found via Help > Release Notes > Is there any way to make this popup appear again? The pop up only appears for automatic compact. For manual compact, use right+click a folder and pick Compact, or File > Compact Folders regarding 20MB setting - personally I recommend a value of 100MB - 200MB

Thanks for pointing this out, Wayne! This explains why I was just asked again whether I want to compact my offline folders. This time, the value is "25.3 MB", which sounds feasible. The size of my profile folder BEFORE clicking on the compact button was 13.220.599.278 Bytes. After clicking the button, the folder size was 13.212.427.796 Bytes.

Unfortunately I'm only on Linux for development. For daily use I'm using Windows. Up to now, The values presented for compatcting have been in a range that sounded reasonable. I never checked in detail though...