What exactly do you think you can open without downloading it first? And what are you trying to achieve in the first place?

Thanks very much CHRIST1 for your reply.

I am trying to open attachments to OWA emails without downloading them.

I used to be able to do this with the Firefox browser.

However when I updated Firefox a few days ago to Firefox 102.3.0 esr (I use Firefox on a Debian 11 system), I found I can no longer open these attachments without first downloading them. This dwnloading procedure is causing a great deal of hassle.

I am looking for a way to continue opening attachments without downloading them.

I found I can no longer open these attachments without first downloading them.

In order to open an attachment you'll have to download it first. There is no way around that. I'll have to guess what you're talking about.

Is it that you get prompted for what to do with an attachment when you attempt to open it? Or get a prompt asking you were to save it on disk? Presumably what you want is that an attachment opens in the corresponding application right away, without being prompted. That is a matter of configuration. You'll have to assign the corresponding application to the attachment file type, e.g. like using Adobe Reader for PDF attachments. See https://kb.mozillazine.org/File_types_and_download_actions

Prior to Firefox 98, one could click on an email attachment and get presented with a screen, giving several options. One option was to open the attachment with an application (a drop down menu was presented to allow one to select a suitable application from a list of applications), while another option was to save the attachment. I understand the attachment would be automatically downloaded to a temporary folder /tmp and the attachment opened from there.

Since Firefox 98, this screen is no longer available and the attachment is always downloaded to the permanent Downloads folder instead of the temporary /tmp folder, irrespective of the attachment's file type. This means that one has to access the attachment in the Downloads folder and then open the attachment with a suitable application. The additional work needed to open an attachment causes a lot of hassle especially when many attachments need to be opened. It also means the Downloads folder quickly fills up with attachments.

I have been using Firefox ESR on Linux Debian 11 to access Outlook emails from Microsoft Exchange via the webmail service called OWA. A few days ago I updated Debian. This caused Firefox to be updated to Firefox 102.3.0 ESR (equivalent to the Firefox 105 main release) and this update introduced the attachments problem outlined above.

I am looking for a way to revert to the behaviour of Firefox prior to Firefox 98. I have tried the various ways to open the attachments as given in a Mozilla support article (a link is given in a related question I recently sent to the Firefox support section).

I don't want to regress to using a version of Firefox prior to Firefox 98 because I would lose important security updates.

https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file#w_what-should-firefox-do-with-this-file-prompt

is the article frommMozilla that I referenced in my previous reply. None of the methods suggested in this article enabled me to open attachments without first downloading them to the Downloads folder.

You can restore the old behavior by setting some prefs in Firefox - see https://bugzilla.mozilla.org/show_bug.cgi?id=1738574#c133

This has got nothing to do with Thunderbird anymore. If there are any more questions, please continue this discussion in the Firefox group.