Do the extensions show as disabled on the Add-ons page (about:addons) or are you merely missing their toolbar buttons ?

Are you possibly using Private Browsing mode as some extensions might be disabled in PB mode ?

• https://support.mozilla.org/en-US/kb/extensionss-private-browsing

as I said, the extensions are disabled - greyed out, with no way of enabling them. (I know what private browsing is, and have couple of extensions enabled in it, but this is not the case here)

Funny thing is, I have a dual-boot (win 10) system, and firefox sync enabled, so both browsers are "identical", but on that "second" ff, everything is ok. All extensions are enabled.

Even if I resolve this issue, it is still bad practice not to warn users about major events like that.

Just clicked update extensions once more, and Last-pass is enabled once more. So it is a case of ff update fudging them...

If you use the same profile with different Firefox installation then this is a recipe for such issues because extensions.json stores the full file path of an extension, so best is to have two separate profile folders and possibly use Sync to sync data.

update 2, I uninstalled decentraleyes, then installed again, this extension is back!

I use firefox sync for ages, and between different pcs, and on this multiboot system without issues. sync extensions was working great, installing same extensions on all firefox installations.

Do You think there is an issue there now (as it was not the issue for many years) ?

edit: I read Your comment again. You do not understand, I use 2 win 10 installations on 2 different partitions let's call them "work" & "games". There are 2 installations of ff on those 2 systems. I use ff sync, to sync bookmarks, history, extensions... etc I DO NOT use same dir for both systems