"This webpage is using significant memory"

I think the difference may be that your newer PC has more RAM (short term, fast access memory, most useful for web use) available than your Mac. You can check the difference. I have an elderly MacBook Air but it copes OK as I had more memory included in the build when I bought it.

My iMac often tells me it's running out of memory and to close some apps. It is 9 years old though so I guess it's getting past it's sell by date. I never thought about FB but I close everything down when I'm done and it's fine the next time I come on it.

Ah thanks NanaMacGeek, I knew I'd be able to rely on you having the right explanation! All makes perfect sense now ☺️

Well, actually, not quite 'all'. I use the web version of FB on my Windows laptop, using the Chrome browser, but never have this problem there. Might that be because my iMac is rather elderly now (6 years old), and is simply less able to cope than my laptop which is a mere youngster, at half that age?

I have had it once or twice. I am using a desktop pc. and am not on Facebook or have any apps on it at all. I just ignored it and it went away.

Facebook is notorious for constant refreshing and activity on its web pages. Apple Macs (Apple) do not provide a 'Facebook app' for their OS X devices, only for IOS (iPad and iPhone operating systems) where there is some ability to reduce drain on resources. So, to use Facebook on an Apple Mac, you have to use the web version. If you know where to find it, you can check how much activity is generated when using FB on your Mac. If you are using FB on a Mac, then close the FB browser tab when you aren't looking at it. That will reduce memory use. The same problem occurs with Chrome browsers.

BradfordLass yes, I've cleared the cache now and deleted unwanted apps etc. I've not been on FB on that device since, so we shall see.

DINNNO no, I've still got masses of storage left.

you might be running out of storage? I also have an apple product and I read in the settings that I have a limited amount of storage until i buy more. So it might be the same with you I don't know

Do you do the 'housekeeping' regularly? Clearing the cache and any downloaded images may help.

I meant to add that it's OK on my iPad and my Windows laptop. It's just the iMac that gets picky with FB. I've just spent over an hour cleaning it up, following some steps on a YouTube video. Hoping that will help, but I'm not holding my breath!

Oh well I'm glad I'm not the only one!

I have that all the time and I don't understand it either! Seems to be okay on my Ipad.