Max number of windows / tabs

There's not a number.

If you're running all the tabs as active, it's possible you just don't have enough resources — depending on what type of pages that is, or, in this amount of content, runaway scripts, GC/CC work, render leaks, addon overhead, userscripts etc. add up pretty quickly. (Not familiar with the specific desktop integrations, drivers and rendering for your distro and windowing environment.)

Did you inspect your content and extension consumption using Task Manager - see whether tabs or extensions are slowing down Firefox for the rough idea?

If you have actual crashes, the patterns could be visible there:

1. Enter about:crashes in the Firefox address bar and press Enter. A list of Submitted (and Unsubmitted, if any) Crash Reports will appear, similar to the one shown below.
2. Copy the 5 most recent Submitted Report IDs that start with bp- and then go back to your forum question and paste those IDs into the "Post a Reply" box.

Note: If a recent Report ID does not start with bp- click on it to submit the report.

(Please don't take a screenshot of your crashes, just copy and paste the IDs. The below image is just an example of what your Firefox screen should look like.)

More information and further troubleshooting steps can be found in the Troubleshoot Firefox crashes (closing or quitting unexpectedly) article.

Thank you for the advise. I submitted the last 5 crash reports, here are the ID's: bp-b2d42d28-fe0a-4b36-af37-f4afc0261007 bp-b29a7e2d-e5a1-49aa-bdf3-c69d20261007 bp-908cc125-50fa-41c8-a1b9-420070261007 bp-57bce800-6eef-460f-b687-eb46f0261007 bp-e7e68496-58af-4596-aa6b-b45e20261007 bp-69de93a4-c213-4105-a13d-0cab20260715

I have looked at about:performance periodically in the past, however, I never see a window consuming a lot of CPU resources. Looking at an overall system monitor, the system (when not set to doing actual work but with all the FF windows open) has the CPU running a lazy 6-8% with GB's of memory still free. No other apps or browsers exhibit this behavior.

I prefer to use FF over other choices so I'm interested in possible fixes.

Appreciate your help!

OK I see this is not performance, resources are a plenty, and the crashes are basically about not being able to launch a (sub)process, or talk to it in lieu of IPC — looks like some rendering speedbump (Nvidia drivers? Image formats / HDR processing? Font rendering? … something like this).

I see there are basically three or four people on the planet crashing in the same spot, on different distros.

Can you for comparison try running in Troubleshoot Mode (from Help menu), for more conservative performance settings and skipping loading any extensions, to see if there's any difference?