All of a sudden...

Thanks for your persistence with this. Whether I can or can't import the correct root CA into FF, I don't know as I've not tried yet, but even if it works, it would mean doing it for every web site that gave the problem! Using Comodo is a far simpler solution!

No it wouldn't, you could import every web server's certificate individually, but that would be a ball-ache.

The alternative is to import the bitdefender root certificate (which you should hope is unique* to your installation of bitdefender) as a trusted CA and then your firefox will trust every "faked" certificate that bitdefender creates on the fly for https sites.

Bearing in mind my computer skills, that still sounds like a lot of arse-ache and angst compared to using Comodo!

No more difficult that the wattsup cert you already exported ...

You could possibly get more support here, I can not remember when I have got a useful answer, often I get no answer.

I contacted Bitdefender with the problem. They recommended I uninstall, download and reinstall it, following their instructions. It went OK until the last stage, when, after appearing to download a new copy, nothing happened, when it should have put up an 'install' instruction. I couldn't find any newly downloaded copy anywhere on my computer. I e-mailed Bitdefender again but so far, no reply.

I'm currently running on Malwarebytes 14-day free trial. If I don't hear from Bitdefender before the end of that trial I'll look for something else. Can you tell me (recommend, even) an AV programme that doesn't mess with SSL traffic?

When I was running windows last, I used Windows Defender and Malwarebytes occasionally. This laptop doesn't work well with Windows10 so it's doing stuff in Linux Mint.

On both my Windows machines, I just use Defender, it's the only AV that's never eaten half my CPU or RAM, it may not get the highest rating in tests, but I regard it as good enough for me, and it doesn't nag to buy extra features I don't want.

Many thanks to both you and Richard for all your advice. If Defender is good enough for you guys, I'm sure it'll be good enough for me.

I have Win7 32 bit, and I see that Defender is part of it. When I open it under control panel, it tells me I am protected. I've ticked all the boxes I can see under the various tools > options to see how it works out for me.

One thing I can't seem to be able to do is to get the Defender symbol to appear in my system tray. I'd like to see it, just to give me confidence that all is working OK. I've tried various suggestions seen on the 'net, such as customising the icons, but it's not showing up there. I've also looked under Tools > Options > real-time protection options, as I read there should be an option there to display an icon in the system tray. But I see no such option on offer.

Any suggestions?

As you're using Win7, there is reduced protection with Windows Defender. See here:

Have you got a little upward arrow at the left end of the tray? I you click it is the defender shield there? Trying to remember the difference between Win7 and Win10, you can probably right click and decide which of the tray icons are shown/hidden

No, nor in the full range of notification area icons. BTDT etc

Right. So it looks as though I want MS Security Essentials rather than Defender, as when run under Win7, the latter only protects against spyware. Thanks for the heads-up.

Ah yes, forgot about the same name for different things ...

I'm guessing you don't frequent dodgy websites so you probably don't have to fret too much. Out of curiosity, how many problems on your computers were detected by Bitdefender etc. in recent months?

Very few, if any!