Every time your browser is updated, there is a possibility that some default action has been changed without you being notified. Every downloaded eBook or map must be saved before you can open it, not every update makes this automatic. If you experience problems or some unexpected behaviour, have a look below for some solutions.

Extensions

I am not recommending these, but there are a number of extensions available (aka a plug in) that claim to enable reading eBooks from within your browser. None of them are from well known developers, but the one that has been around for some time is EPUBReader. In my experience, it must be temporarily disabled whilst you save files.

To do this, go to "Settings" then "Extensions" then "EPUBReader" and turn the blue slider to "off".
You also need to go into "Details" and tick "Allow access to file URLs".
Download and save the file, then turn the blue slider on again.
Find the file then "Right click" and "Open with" Chrome or Edge.
This currently does not work for me with Firefox.

Google Chrome

If you use the Chrome browser and are having trouble downloading zip files or eBooks, look at the box that appears in the bottom left-hand corner of the screen and click the tiny up arrow ( ˄ ). If "Open","Open when done" or "Always open files of this type" are ticked, untick them.

You may also need to change the way Chrome handles PDFs. Go to:- Settings > Advanced > PDF files. Then enable "Download PDF files instead of automatically opening them in Chrome".

If that does not help. Go to:- Settings > Advanced > Downloads. Then enable "Ask where to save each file before downloading".

Windows Edge

The default for downloading using Edge should be set to save files in the "Downloads" folder. When this is complete, in the box that appears in the bottom left hand corner, you will see a link to "Open file". Do not click it, in case it has not been saved.

Click the three dots in the box and then click ''Show in folder'' to make sure it is saved. Open it from there with your chosen program or move it to where you want to store it.

Using "Settings", you can change the default folder and/or make Edge ask you where to save files.

Firefox

The default for downloading using Firefox is set to save files in the "Downloads" folder. Whilst this is happening, a "down arrow" icon appears in the top right of the tab. When this is complete the icon turns blue and you can click it to see the file.

Settings can be changed using the Applications tab in Firefox's Options.