Have a working group of 88 sites I open after starting Firefox. Usually takes 2-3 minutes tops for all to be readied. Now taking 10-12 minutes or more. Just last few days. ... ODD Note: If I open the 91 ESR profile, then Startup Cache folder, clear the cache from about: Support, it does not delete the files. Yet that IS the profile being used. On at least one of the portables, that works as expected. If I delete the Startup cache files and open FF 91 ESR, it does not rebuild them. Makes me think it is using a different profile, but I am sure it is not. I cannot try Safe Mode as the Session Manager would not be there to open the saved session. I may try turning off some Add-ons to see if a conflict, maybe with something added or updated recently.

At first, I thought this was a problem with the built-in session restore feature. With that feature, by default, Firefox only restores the content of the active tab in each window and when you click a different tab, you need to wait several seconds (sometimes longer) for it to load. This can be changed to load all the tabs at startup and of course with over 80 tabs that would be miserable.

But you mentioned that you load them from an add-on. The add-on may have an option to follow Firefox's approach of deferring loading tab content until you activate a tab, or it may require Firefox to load the content immediately. I don't know whether you have changed that, or the author changed that, but I think it's worth checking that it remains the way you want.

I didn't think the "Startup Cache" was used for web content, so I don't know why clearing it would help in any cases. If you were to clear the web content cache (using the Clear Data button on the Settings page), then instead of Firefox trying to rebuild your restored/reopened tabs from the disk cache, it would go to the original URLs. Depending on the relative speed of your internet connection and the speed/fragmentation of your hard disk or SSD, the network might be faster. Hard to know without testing.

If up to now you have been relying more on the disk cache but now Firefox is not able to use it for some reason -- for example, Firefox is clearing the cache when it closes or Firefox is crashing, which invalidates the cache -- then that might explain the difference.

Web content cache and "Delete cookies and site data when Firefox is closed"

In Firefox 102+, this feature has changed and now cache is linked to clearing cookies and site data. However, this definitely was not added to Firefox 91, so it's not relevant to your scenario, I don't think.

Hmm, actually, on that last point, if you Sync Firefox 91 with Firefox 102, maybe all three of them are clearing the cache. Check your Settings page, Privacy & Security panel, History section. If there is a checkmark for "Clear history when Firefox closes", click the Settings button to the right and see whether Cache is set to be cleared. You can uncheck it here.

Thanks for the thoughtful replies. A lot ot repond to:

Let me mention a few other things first.

I uninstalled and reinstalled FF 91 ESR with no change. Using Recommended memort settings and/or Acceleration when available makes things much worse. I nver use (for years when all working) "lazt tab loading" either in the Add-on or FF.

OK: 1. Not built in session restore. I have MANY sessions, but this one used several times every day. 2. In FF 91 ESR Portable, the startup cche DOES clear as expected and no postivie chnge for the loading issue. What is odd is that it does not clear in the installed 901 ESR version. 3. Hmmm, I doubt its a disk cache issue. But maybe one thing I can try there. I do not have it set to clear upon closing - unless an update changed that. Will have to reply on results from that. Agree the difference in 102 should not make a difference to 91's that changed 48 hours ago. 4. I manage my cookies carefully. Have an addon to delete the ones I dio not wish to keep and keep the once I need. Have been doing that for years as well. 5. I do not sync profiles with 91 and 102. 102 started with the same profile as 91, but only synce the 91 and 91 portable.

Will check cache. But if not, still very stumped.

~Bob

OK, I have ALWAYS cleared my cache when FF closes. ALways. Especially when things worked well. Tried not clearing and no improvement. Maybe even worse. Though I vaguely recall a setting to check for new versions of a page each time loaded, but not sure where that is.

~Bob

Thought I had something, but alas , no.

The installed 91 ESR showed two profiles. One did not exist and was not shown as default. I removed it. No change :(

BOTH portables show the installed version profile as its only, but not as Deafult. SO likely it sees the installed profile but uses the portable's folder.

I check and BOTH disk cache and ram cache are enabled. RAM set to -1. I never see anything in the Cache2 folder.

Portable has its own file structure and profile behaviors, so I don't know much about what it does.

If you always clear cache at shutdown, then Firefox needs to load everything from the network when restoring your session (or opening pages from other lists such as your add-on). There may be some recent changes in connection settings in Firefox 100+, but nothing has changed in Firefox 91 ESR except the very few things you would find in the release notes (https://www.mozilla.org/firefox/releases/).

How about external factors: security software filtering your connection, proxy server/VPN, or any other intermediaries.

Thanks again.

Belive it or not, after using Firemin for YEARS, turning it off helped immensely. I also think recnt updates to ESET NOD32 AV have an effect here, but I have not found that one yet.

Belive it or not, after using Firemin for YEARS, turning it off helped immensely.

I have not heard of it before. If the program works by cutting off physical memory usage, that could force use of the Windows swap file, which is way slower than physical memory. But I have no idea what's really going on there. You could post on their Issues: https://github.com/rizonesoft/Resolute/issues

Thanks, but no nmeed to contact them. Firemin has not changed at all. But I strongly suspect the update to Firefox or "possibly" Windows 10 for memory management DId change. And so Firemin was no longer productive and trathe damaging performance! With it removed I am running as I think I shoul dbe. Hard to find!!

My clue was that CPU was pegging, not RAM. So taking away that RAM management allowed the CPU to relax.

I got lucky....

Thanks for the help!