Basically housekeeping for user data that use temporary or transient storage files while Firefox is running. When the user closes Firefox the data that is in those transient files gets saved to their "permanent home" files.

As far as Firefox crashing when you close it - that shouldn't be happening. And when Firefox does crash there is always the risk of user data getting lost. As far as you using an older Firefox 38.0 version - not normal for Firefox to crash upon closing. Never happens for me with the Firefox ESR 38.7.1 version (on Win7) that I still use everyday. I open and close Firefox ESR as often as 10 times a day, and it has never crashed upon closing. And about the only time it crashes at all (or goes unresponsive) for me is when Flash is running.

the-edmeister said

Basically housekeeping for user data that use temporary or transient storage files while Firefox is running. When the user closes Firefox the data that is in those transient files gets saved to their "permanent home" files. As far as Firefox crashing when you close it - that shouldn't be happening. And when Firefox does crash there is always the risk of user data getting lost. As far as you using an older Firefox 38.0 version - not normal for Firefox to crash upon closing. Never happens for me with the Firefox ESR 38.7.1 version (on Win7) that I still use everyday. I open and close Firefox ESR as often as 10 times a day, and it has never crashed upon closing. And about the only time it crashes at all (or goes unresponsive) for me is when Flash is running.

Thanks!

To clarify, it only crashes when there's a lot of memory used up by FF.exe and the flash plug in.

I have disabled hardware acceleration since installation in fact.

I did add the Video Downloadhelper add on last week, which might exacerbate the situation.

Btw, FF is not clearing cache on exit, is there a way to do that automatically? Also, the default size is 300 MB I believe, does it make a difference to change that?

Forgot to ask you, is it worth it to try Firefox ESR 38.7.1 and where would I safely find it?

Having the cache clear on exit might exacerbate the crashing issue; more 'housekeeping' to do upon closing.

Did you go to about:crashes and then open the Crash Reports to see why Firefox is crashing?

Overall, I can "feel" when Firefox is about to crash and I restart it before it actually crashes. You can also look at the Windows Task Manager and see how much 'memory' Firefox is using, and once you get a feel for it you use that to know when Firefox 'needs' to be started. Catch it soon enough and the Restart will reload all the Tabs that were open. Wait too long and the Restart may 'drop' the most recently opened or used tabs due to Firefox locking up.

There are many extensions that add a Restart button button to Firefox. https://addons.mozilla.org/en-US/firefox/search/?q=Restart That Restart feature is also accessible from the Developer Console, but needs command line to use it; although I can't recall if that made it into the Developer Console in Fx 38 or not - I have never used it from there.

Look for an extension that is specifically compatible with Firefox 38 - will be labeled "Legacy" and may be labeled "Requires Restart" which would make it a non-SDK Legacy extension. iirc, probably developed before Fx 29 Australis came out.

Here is the last 38 ESR version, which has security updates equal to what Firefox 46 & ESR 45.1 had: http://ftp.mozilla.org/pub/firefox/releases/38.8.0esr/win32/en-US/

I can't recall why I didn't update to that at the end of April 2016 when that came out.