Firefox Developer exhausts system resources

One week after reinstalling mainpc I had a repeat of the situation that caused the reinstallation. Firefox Developer, which is the main browser I use, somehow got into a situation where it was using full CPU, RAM and swap for a period. I use the KDE system load monitor widget on the panel to monitor what the system is doing on my computers that have KDE. The system slowed right down and I noticed all three bars on the widget were all the way up. After a period of the system being bogged down and almost impossible to use due to being maxed out in resources, Firefox Developer crashed (or at least the instance that has the most tabs open, the other instances stayed open) and then the bargraphs all dropped to almost nothing.
Unlike the previous occasion the /tmp space was not all consumed so everything is still working properly. Possibly this is because I put /tmp onto its own partition and possibly also because the system had 100 GB of swap available after the reinstall. All the disks had the usual amount of free space available.
When Firefox was reopened there were no obvious issues and the resource use stayed low. However it is worth noting that the open tabs won’t all be reloaded at startup, they are reloaded when they are clicked on. I did go through them later to reload and saw no issues with resource use.
It looks like there is some sort of scenario where Firefox can “run away” and crash after using up all the free resources. The whole thing is a bit bizarre but it has happened twice in one week and so I will have to see what I can do to try to find out exactly what is going on. But this could be quite hard to achieve. However I can guess that it probably leaks memory. It probably doesn’t release or reuse memory used by a tab when the tab is closed, so it eventually uses up all the memory in the system, crashes and releases it all, then when it reopens, of course it doesn’t need all that memory that it had.
The thing you see in KDE’s system activity monitor if you open it up (press Ctrl and Esc together) is a few processes called firefox-bin which are the individual browser windows, and a number of processes called Web which don’t mean a lot but are using significant amounts of memory, CPU or whatever. When I dig further in, Web  turns out to be using Firefox library files, so it must have something to do with Firefox. The common factor in most cases is using, a library that is installed as part of Firefox Developer. 
At any rate this seems to be yet another example of the enormous resource hog that web browsers just seem to all be by default. All the tabbed ones seem to just use ridiculous amounts of memory in the computer.

UPDATE: The process that crashes is called Web Content (as top shows it) and it may only crash a tab rather than the whole browser. I currently have a bug report lodged into the Bugzilla database to see if it can be addressed as a bug in the browser, as I have been able to replicate this with one particular web site which crashes Firefox Developer every time.