You can try to use the "Free Memory" feature on the about:memory page to see if that works.

I tried that but it didnt work. If I restart Firefox then it obviously works, but I was hoping that there was a coding type fix?

Does it help if you disable Firebug?

Start Firefox in Safe Mode to check if one of the extensions (3-bar Menu button/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: 3-bar Menu button/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

disabling all the add-on's reduces the total memory used, but still doesn't release the memory when the tabs are closed

What is taking up that memory if you check that in about:memory?

cor-el said

What is taking up that memory if you check that in about:memory?

I took two measurements both when the tabs were open then closed, can I attach them with the Add images button

I thought I would post some Background Info on about:memory for you to look at whilst waiting for cor-el to get back to you.

You may add them or parts of them using add images if you take a screeenshot. It is also possible to select parts and paste them into the forum as the display is text, but that may distort the formatting, and so linking to a copy of the text file may be a better option.

Take CARE: you may wish to review for any sensitive or confidential info before posting anything from about:memory

Also note about memory has a diff function. You may be able to use that to isolate the memory increase by doing a diff before and after opening the troublesome tabs. See Also

• diff: https://blog.mozilla.org/nnethercote/2013/04/26/recent-aboutmemory-improvements/
• Tutorial https://developer.mozilla.org/en-US/docs/Mozilla/Performance/about%3Amemory
• KB article Firefox uses too much memory or CPU resources - How to fix_memory-troubleshooting-tools

Note also that the files will save as gzip format that may be convenient for transferring the full info but this forum is unable to handle the files. You could consider placing the files on https://pastebin.mozilla.org/

John99 said

I thought I would post some Background Info on about:memory for you to look at whilst waiting for cor-el to get back to you. You may add them or parts of them using add images if you take a screeenshot. It is also possible to select parts and paste them into the forum as the display is text, but that may distort the formatting, and so linking to a copy of the text file may be a better option. Take CARE: you may wish to review for any sensitive or confidential info before posting anything from about:memory Also note about memory has a diff function. You may be able to use that to isolate the memory increase by doing a diff before and after opening the troublesome tabs. See Also

• diff: https://blog.mozilla.org/nnethercote/2013/04/26/recent-aboutmemory-improvements/
• Tutorial https://developer.mozilla.org/en-US/docs/Mozilla/Performance/about%3Amemory
• KB article Firefox uses too much memory or CPU resources - How to fix_memory-troubleshooting-tools

Note also that the files will save as gzip format that may be convenient for transferring the full info but this forum is unable to handle the files. You could consider placing the files on https://pastebin.mozilla.org/

thanks for this, I've saved two memory files so I'll do a diff between them to see if I can see anything interesting,

Does about:memory use JS to run? If I run 4-5 about-memory in a row the memory increases between 50-100mb each time and then stays at that level until I quit Firefox. How do I disable JS in firefox, then I can try and run multiple tabs and see if the issue is as pronounced?

Final question for now. What's the correlation between About:Memory Explicit Memory and the Memory recorded in Mac's Activity Monitor? When I had very few tabs open the difference between the two was about 30mb, when I opened lots of tabs this gap widened. Even when I then closed the excess tabs, the difference between these two numbers was >100mb? Is it possible that the Mac Activity Monitor doesn't record this number accurately for firefox, or at the least different than the way firefox handles it?

thanks

It is probably best to wait for cor-el to get back.

My thoughts are that it may be better to ask yourself: Are you getting problems that are thought to be caused due to lack of memory ? and resultant paging ? Rather than place too much emphasis on what the actual figures are. Unless you find say one specific site or one particular addon causes Firefox memory to keep on going up untill Firefox hangs or crashes.

The about:memory live display has tooltips that show up on mouseover. It explains some of the categories. Yes I believe Macs may show different results to Firefox's about memory.

I'm not on a Mac, so I don't know how all those tools work. Interpreting the data that shows on about:memory is not easy and I'm not familiar with the details as well.

I came across a link to an article about the activity monitor that might provide some information. Use Activity Monitor on your Mac - Apple Support: https://support.apple.com/en-us/HT201464