Originally I was using 18.04 LTS.
I thought it would be good to update to GG (20.10) though I did briefly try FF (20.04).
As the install was done on an existing 18.04 version things remained the same for programs, book marks, etc.
Ok, now the crunch: I USE Firefox A LOT. When it loads, there are...... 8 x 6 windows of FireFox and each of those have anywhere from one to THIRTY tabs loading.
Believe me: It worked!!
I could use it, also run other tasks as well - though a VM was pushing it with the RAM. But the entire machine worked.
Now, I am lucky if FireFox loads at all. Let alone let me browse.
When it loads some of the window's tops are flashing. A screen shot does not really show this. (I tried)
All that has changed is the O/S from 18.04 and Firefox from (what ever it was) to 83.0
I don't want this to be a finger pointing exercise between Mozilla and Ubuntu. I would prefer it is helpful to all.
What have I tried? I've tried starting FireFox with all addons disabled. Still happens.
I am going to try to remember to (next time) launch FireFox from a Terminal and pipe the output to a file to look for things.
The machine I am using has shown it is well up to being able to have this running. I have had it working for a few years like this.
This post is (for now) to establish there is a problem. I will post more information when I get it, rather than waiting to get it then post, as I feel there are a lot of people who have very similar problems and I want it known: You are not alone!
monospacefont and line breaks need to be retained so we can parse the data correctly. You will achieve a better response and will be more likely to find an answer if you take some time and compose your question right from the beginning. It doesn't help anyone to post like this. We aren't running out of spaces for new questions.