Hi, sorry there is not. You used to be able to install the Extended Release Version but starting next month that is no longer possible. Am not sure if can on the last version.

That's such a shame: I've been a loyal Firefox user and supporter since the day it was born, but I send so many emails per day with many attachments that I don't think I can live without a 'silverlight' type of add-on. Unless there is an alternative to Outlook? :)

Hi, there is always Thunderbird : https://www.thunderbird.net/ You can give the portable version a try : https://portableapps.com/apps/internet/thunderbird_portable

Chrome has not supported Silverlight for ages, Firefox stopped last year and there is no support for it in MS Edge in Windows 10 as I am sure you noticed. So when they drop IE there will be no use for it any longer. It is also not been actively updated since 2012 and is a security risk.

Many Office365 plans come with the Outlook desktop app, which is going to give you the best functionality and compatibility for heavy use.

Unfortunately, the "Business Essentials" plan doesn't include the Outlook app, so you're limited to web.

But where is the problem in your workflow? Let's say you want to attach several files from a particular folder to a message in Office365. You can multi-select files in the folder using either of the usual methods:

• click the first file then Shift+click the last, for a continuous range
• Ctrl+click each file

When I use either of those methods, Firefox lists all the individual files names (in quotation marks) in the File Name field and when I click Open, Firefox uploads all the selected files.

I do think without a plugin, this will only work in one folder at a time. If you need to add files from a different folder, that would require another visit to the paper clip icon.