FALSE ALARM, CULPRIT FOUND: I had a MalwareBytes browser extension that slowed the emote picker down. The extension has been purged and now both the popup and the inline picker are working well.
The original post before I did testing
I try to 
in a Hexbear comment. The picture takes forever to even load in the picker so it takes a while to see if I've even selected the right emote. Most of the emotes in the list I can't even see the pictures unless I step away for a minute and come back after they've all loaded. I hit submit comment. It takes forever to post. I can hear the fans whirring. If I'm streaming vid on blorptube while posting something from the emote picker, sometimes the video will just pause and stop loading until whatever process the emotes have kicked off completes. I don't know why some emotes are visible while others aren't it doesn't appear to be related to order that they show up in the list
I think "Well I'm on the ESR of Firefox, maybe it's just old" but then I boot into Linux with cutting-edge up to date Firefox and it still behaves largely the same.
I have wondered if it's an internet speed thing but it seems to behave this way whether I'm on ethernet or 802.11n wireless, whether or not my VPN is on.
It also takes quite some time for emotes to load in the emote picker on Blorp, come to think of it.
I've got 16GB of RAM, that should be plenty. Yes I know the web has gotten more intensive since this computer was made 13 years ago but come on, compared to hell sites like twitter, facebook, and new.reddit, lemmy seems downright lightweight. NoScript and other blockers aren't blocking a ton of bloat here.
I'm not criticizing the unsung heroic devs of Hexbear. I'm no good at web dev, hated it when I had to do it for work, and couldn't fix or optimize this either. But I would like to understand what the root cause of this problem is and
(If the answer is "upgrade your hardware or live with it" then I'm living with it, because my precious little computer is my buddy and I'm not abandoning it)
When you refer to the emote picker, do you mean the one that pops up when you start typing out the shortcode (e.g. :fidel ) or the one above the text input box under the little smiley icon?
Both have performance issues to some degree, but there probably isn't much you can do on your machine about it. Maybe there's some sort of extension that can force cache them? It's something we've tried addressing from the server side in the past with limited success, but it could use more work.
I mean both. Here's a pic of what I see 2 seconds after clicking the smiley icon:
Here's a pic of what I see 2 seconds after typing ":fidel-" in this comment input field:
If there's nothing I can do about it because it's server side then there's nothing I can do about it. Ultimately it's a minor annoyance. I tried glancing through the Hexbear code on Github to see if I could try to diagnose the problem and all I got from it was a reminder that I am terrible at web dev.