Hello, thank you for your comprehensive reply! The patch has fixed my kill_sticky version which I got over a year ago from an unknown source. Indeed I was transplanting a FF52 profile but then started a clean one and the extensions would not install either. The other problematic are: cookie_autodelete-2.2.0-an+fx.xpi and export_cookies-1.2.1.xpi. I think cookie_autodelete can be patched like kill_sticky but export_cookies is different, it declares <em:maxVersion>3.6.*</em:maxVersion> which should be ignored with
user_pref("extensions.checkCompatibility", false);
user_pref("extensions.checkCompatibility.52.9", false);
user_pref("extensions.checkCompatibility.52.9.0", false);
but it is not. Works in FF52. Should I look for an alternative addon?
EDIT
On AMO site they show "This add-on requires a newer version of Firefox (at least version 59.0). You are using Firefox 52.9."
I have
user_pref("general.buildID.override", "");
user_pref("general.useragent.override", "........Firefox/68.0");
How do they detect it?
EDIT2
I got it, need to add these:
user_pref("general.useragent.override.accounts.firefox.com", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.9) Gecko/20100101 Firefox/68.9");
user_pref("general.useragent.override.addons.mozilla.org", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.9) Gecko/20100101 Firefox/68.9");