Yeah, I'm disinclined to believe that
Tried it myself (Firefox 98.0.1)
The Slack tab uses 7/8MB - but that figure comes from Firefox's own task manager. Firefox's process exposure to Windows is a load of arse - just nine "Firefox" processes, using between 2 and 250 MB each. Helpful.
The Windows task manager tells me that Firefox as a whole, running nothing but the Slack tab, is using 605MB, which is congruent with both Chrome and Edge.
The Slack tab uses 7/8MB - but that figure comes from Firefox's own task manager. Firefox's process exposure to Windows is a load of arse - just nine "Firefox" processes, using between 2 and 250 MB each. Helpful.
The Windows task manager tells me that Firefox as a whole, running nothing but the Slack tab, is using 605MB, which is congruent with both Chrome and Edge.