I like this forum a lot and I've learned a lot here, but unfortunately it is getting slower and slower... and it's not my browsers or equipment problem. For more than a week, I've been trying to change my signature every day and I can not do it in any browser. I know ads, pops and pubs support this, but I agree with what chris1111 said...
Edit: Ok, the page today opened normal and I was able to edit my signature. Thanks
This is an old security update. It released on Mar 29, 2018.
As I said there is no any security update for Sierra at Apr 24, 2018, you can see the all update list in this link;