The answer is basically the same for Firefox and Thunderbird.

The Firefox discussion is here and much better illustrated than the Thunderbird article. https://support.mozilla.org/en-US/kb/make-firefox-your-default-browser

Enough to say repeat the 1st step of click of menu button on Thunderbird and select options. Then select the advanced tab. On the general sub tab click the check now button.

Matt Thanks for your reply, but unfortunately it does not solve my problem. MS Windows 10 Pro Version 1709 does not provide the option of making Firefox the default browser. Firefox is neither listed in the default browser options (as stated in the article to which your referred) and it is not listed in the App Shop options. It is not possible to re-instate Firefox as the default browser when MS Win 10 does not provide it as an option. I am not the only user who has recently noted this fact.

Windows 10 Home Edition apparently needs a different approach or doesn’t allow changing the default browser to a non-Microsoft browser easily or at all, possibly for marketing reasons.

Another person had similar issue but resolved it: https://support.mozilla.org/en-US/questions/1166218

Sometimes a complete reinstall of Thunderbird / Firefox works.

But I would first try this: 'Start' > 'Settings' > 'System' > 'Default Apps' > 'Set Defaults by App' click on Thunderbird, then click "Set this program as default".

Dear Toad Hall Thank you for your reply. I have previously tried every imaginable direct and indirect method (both via "settings" and "Control Panel") for setting Firefox as the default browser, but the Firefox option IS NOT available. I have also uninstalled and re-installed Firefox, but Win 10 Pro still does not include the Firefox option. (Please note that Thunderbird is an option in Win 10 Pro.) Nevertheless, I re-tried you suggestion and still discovered no option for Firefox. Am I missing something? Why is MS allowed to indulge in this anti-competitive behaviour? Any other suggestions or comments would be most welcome. Thanks

Windows 10 has some annoying habits :) Have you tried: 'Settings - Apps - Default Apps' there's a clickable 'set defaults by app' option.

Found this tutorial: www.tenforums.com/tutorials/5507-choose-default-apps-windows-10-a.html

TRy the option 5 https://www.tenforums.com/tutorials/5507-choose-default-apps-windows-10-a.html#option5

Is Firefox listed under: Win+X->Control Panel->Default Programs click on "Set your default Programs" click on Firefox then "Set this program as default" https://www.tenforums.com/browsers-email/50094-firefox.html#post667522

If firefox is just not appearing in any list: Uninstall Firefox, download the browser again and reinstall. Run and Hit the option to make it the default browser when Firefox first opens, and hopefully this time Firefox will be on the list.

There used to be a way of accessing the Control Panel > Default Programs> 'Associate a file type or protocol with a program' But I'm reading info that this is not necesarilly available under Windows 10.

I've located a link that may help you to get this view again. https://community.spiceworks.com/topic/2074004-windows-10-fall-creator-s-update-where-my-default-program-settings-at

Basically: Press "Windows" and "R" to get Run Paste in: control /name Microsoft.DefaultPrograms /page pageDefaultProgram

press 'Enter' This should get the access again.

Assuming Firefox is in that list...set all the following to 'Firefox'

• .htm
• .html
• .mfp
• .shtml
• .xht
• .xhtml
• .xml

Protocols

• FTP
• HTTP
• HTTPS

Dear Toad Hall Thank you very much for your effort. Unfortunately, I have previously and unsuccessfully tried variations of all the suggested fixes. I have just worked through them yet again, but the problem persists in that Firefox is never an option listed in Win 10 Pro. MS simply does not want Firefox working in the system as a default programme. Given that MS Edge (the default) is a very clumsy and inferior programme it is a seriously limiting situation for the both user and Mozilla. Thank you yet again for your efforts! Regards

The image is probably huge, but it is taken from my Windows 10 professional system Version 1709 (OS Build 16299.309) just now.

That you are having issues leaves me thinking

1. That you are not a local administrator and are not installing the software as such, hence the relevant parts of the register are unavailable for update.

2. You have software on your system that claims to be security software that is blocking updates. The normal advice is to install in safe mode of the operating system to test if that is a possible cause. Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Windows 10, instructions to start in safe mode are located on the Microsoft web site at the link.

3. You are not enabling updates to the system when prompted using an administrator password for Windows. If you are unsude of the UAC prompts. See images of UAC prompts window at point 5 here https://www.windowscentral.com/how-bring-back-old-user-account-control-prompt-windows-10

Dear Matt

Thank you for giving detailed consideration to my problem.

First, I am logged onto the machine as a Local Administrator and If I run any files, I run them as an Administrator.

Second, I am aware of UAC prompts and I have clicked on any that appear and request permission to install Firefox. I must admit that I have not read the UACs carefully and will do so in future.

Third, I will uninstall and re-install Firefox tomorrow (when I might have some spare time), after putting the machine into Safemode With Networking. This seems to be a very good suggestion.

Many thanks for your help Cymbid2

Dear Matt I have tried your suggestion of re-installing Firefox in Safe Mode.

Whilst in Safe Mode, with Networking, MS made it very difficult to use either MS Edge or MS Internet Explorer (Firefox being un-installed) for the task of downloading Firefox. Both browsers refused to log onto the Firefox site and I could not change Bing to another search engine. (This may have been possible, but I gave up after wasting considerable time attempting to do this.) I finally went to another computer and downloaded the full programme onto a USB stick. I re-loaded the programme onto my PC and attempted to set Firefox as the default browser. Yet again, MS Win 10 did not provide this option. I was essentially back in the same situation. Nevertheless, your suggestion was a good one and I needed totry it.

Meanwhile, MS Win 10 has been providing me with messages, on the side of the screen, telling me how much safer it is to browse the web with Edge rather than Firefox. It is obviously a very detailed and effective campaign to stop MS Win 10 users from employing Firefox.

Thank you again for your help. I wonder what the official Mozilla policy is in respect to this MS behaviour?

Regards cymbid2

I've located some info which mentions that recent Windows update has preset conditions for eg: Microsoft Family Features blocking Chrome and Firefox. For some reason Windows is automatically blocking a lot of browsers including Chrome and others like it all you need to do is simply unblock those web sites.

Perhaps this may have something to do with blocking Firefox.

official response seems to be : From the latest family features update: Most commonly used browsers don't have web filtering. To keep your children safer, we'll automatically block these browsers on their devices.

• https://answers.microsoft.com/en-us/windows/forum/windows_10-win_family-winpc/microsoft-family-features-blocking-chrome-and/4b7dad49-eaf9-4c7a-9cf9-5fe06552fd8d
• https://answers.microsoft.com/en-us/windows/forum/windows_10-security/windows-10-family-safety-web-filter-not-working/88011afd-88bf-4f25-b252-715cd3112046?page=2

Dear Toad-Hall

Thank you for this information concerning MS "Family Safety" or "Family Options".

I have checked my settings for MS Windows Defender (and the Control Panel), but I cannot see any setting that could be either directly or indirectly blocking my use of Firefox. I have, however turned off "Check apps and files" in Apps and Browser Control. This change has not (yet) brought back my control over Firefox as default browser. I suspect, however, that this "Family Safety" issue is part of the plot for MS to prevent Win 10 users from employing Firefox as their default browser. It is a convenient excuse to state that it is a family safety issue.

It is a remarkable coincidence that I have been recently receiving messages on the edge of my MS Edge browser telling me how much safer MS Edge is compared with Firefox. These messages were not related to family safety, but at my use of Firefox as a non-default browser.

Thanks and regards Cymbid2