Firefox has lag issues when 6 windows are open with over 12,000 tabs open

Currently I have 6 Firefox windows open:

1. Window 1 has 12,142 tabs open
2. Window 2 has 129 tabs open
3. Window 3 has 1 tab open
4. Window 4 has 42 tabs open
   
5. Window 5 has 64 tabs open
6. Window 6 has 92 tabs open

The majority of the tabs are in the "unloaded" state so they should not be taking up any CPU time.  

RAM usage is less than 50% and CPU usage is on average less than 50% across all cores. 

I am running both Firefox and Chrome at the same time and Chrome is significantly more responsive.

Even something as simple as opening a new tab in Firefox takes a few seconds, whereas opening a new tab in Chrome is instant. To be fair, I only have 300 tabs open in Chrome right now, but this shows that the performance issues are not due to my hardware.

Creating a new tab in Firefox and then entering a URL then hitting enter, the tab takes a while to even begin loading the page. 

Even while writing this blog post, every few seconds while typing, the text just freezes for a couple of seconds before my keystrokes make their way onto the screen. I notice this when typing on monkeytype and typeracer too - sometimes the text just freezes for a few seconds. This happens almost every other sentence and it only happens on Firefox and not on Chrome.

When watching a YouTube video, every few seconds (say 5-20 seconds), the video just freezes for a couple of seconds while the audio continues to play. Again, this ONLY happens on Firefox and does not happen on Chrome.

I think this issue started to happen from a while ago but recently the lag just got bad enough to the point where it is actually impacting my monkeytype performance, so I decided that I had to close some tabs. 

But before closing my precious tabs, I have to save them somehow. Here is where I ran into problems. 

It turns out that Tab Session Manager no longer works when you have 12,000 tabs open.

Tab Stash also doesn't work when you have so many tabs.

Firefox's built-in "save all open tabs as bookmarks" works, but does not save tab state and history, which is desirable.

So I'm going to try to find a way to just save my Firefox "profile" somewhere so that I can restore it later along with all of the tab state and history.