Download Manager (S3) by Oleksandr

Since version 5.1, Download Manager (S3) is now fully compatible with WebExtensions (Firefox Quantum 57+) and Google Chrome
the latest XUL version for older versions of Firefox, SeaMonkey and PaleMoon is here: https://addons.mozilla.org/addon/s3download-statusbar/versions/4.13

Original Download Statusbar add-on for Mozilla Firefox is abandoned October 28, 2011: https://addons.mozilla.org/firefox/addon/download-statusbar/

Does it mean its death? Of course not! It has been reborn! I brought it back to life!
Now it is called Download Manager (S3) and works with all Firefox versions 26+

Completely rewritten code to be compatible with the latest versions of firefox, but visual interface unchanged for use as a familiar old Download Statusbar

What is Download Manager (S3)?

Despite its compact size, Download Manager (S3) packs in more useful features than the standard download window. The fully customizable interface auto-hides when not in use, allowing full control without interruption.
HotKey:

• Ctrl + J = Open Download History page
• Ctrl + Shift + Z = Show/Hide Download Bar
• Ctrl + Shift + Backspace = clear the last downloaded item
• Ctrl + Shift + Insert = Undo last clear
• Ctrl + Shift + Enter = open the last downloaded item
• Alt + Shift + Enter = show the last downloaded item

New Features (compared with the original Download Statusbar):

• Replace Downloads Library page.
  Now you have full control of your downloads history!
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  Features:
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  show progress, time remaining, full file path, url, etc..;
  show summary progress;
  for one download or groups: retry, pause, cancel, resume, etc..;
  search in Downloads History;
  preview image files;
  and many other functions
• Show only NUM completed downloads
• Checksum for downloaded file
• Checksum for any file
• Position of the buttons in Download bar (left or right)
• Hide Download bar when all downloads are completed
• Show special icon if the file not found
• Place newest downloads from: Left or Right
• Download bar in top of the screen
• Options: Text Sizes - Tooltip Size
• Queue Mode
• Show the 'Downloads Completed' notification
• Summary progress on Download bar
• ...and a lot of other changes

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Download Manager (S3) for Google Chrome: https://chrome.google.com/webstore/detail/download-manager-s3/ngmcjenopiialholjggicgplegmcmjda
WebExtensions Limitations:
1. Download Bar not displayed on some sites from mozilla.org and google.com
2. Download Bar not displayed on sites that do not have pages, for example error 404 (page not found)
3. Download Bar not displayed on internal Firefox and GoogleChrome pages, for example about:addons , about:config , chrome://extensions/ , chrome://settings/ , etc.
4. Download Bar not displayed on the extensions pages "moz-extension://...." , "chrome-extension://...."
For display and normal work on the pages of addons.mozilla.org, only for Firefox Quantum 57+
1. in the address bar: about:config
2. right-click to create a logical
3. setting name: privacy.resistFingerprinting.block_mozAddonManager
4. value: true

Mozilla changed the functionality in Firefox 60. Firefox 60 comes with a new preference called extensions.webextensions.restrictedDomains which lists domains that WebExtensions are not permitted to run on by default.

1. load about:config?filter=extensions.webextensions.restrictedDomains in the Firefox address bar
2. remove one, some or all of the domains listed under value to remove the restriction

you do not need to restart the browser, just update the tab addons.mozilla.org

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Download Manager (S3) is full compatibility for Google Chrome, but there are known problems for Firefox:

1. downloadItem.exists does not change from true to false when a file is removed https://bugzilla.mozilla.org/show_bug.cgi?id=1381031

2. does not display history from past sessions https://bugzilla.mozilla.org/show_bug.cgi?id=1255507

3. chrome.downloads.drag is not a function https://bugzilla.mozilla.org/show_bug.cgi?id=1245648

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forums mozillaZine: http://forums.mozillazine.org/viewtopic.php?t=2793995

forums mozilla-russia: https://forum.mozilla-russia.org/viewtopic.php?id=73317