5333 private links
This sounds like a typical problem of visiting a site that does dynamic updates of content but never actually reloads the document, leaks all over the place, and combined with leaving the browser open ON such pages for days or weeks (and even restored sessions may have bloat in the saved viewers), making the garbage and cycle collectors run out of headroom. The pauses in that case are caused by non-incremental GC/CC runs trying to recover resources but failing because the websites are such slobs that they keep a lot of resources locked.
A restart of the browser would fix this kind of thing, so if you changed extensions and issued a restart as a result, that would clear the problem. Even disabling a restartless extension could temporarily alleviate the issue giving you a red herring because it would give the browser a little extra headroom -- until that fills up too and you end up back under memory pressure (heap memory is usually not the problem here, but stack memory would be and that is limited) with the collectors trying their best to recover and failing to make a dent, then trying again, etc.
To analyse this kind of thing, about:memory reports usually give a good indication of the culprit sites. In a more limited fashion, about:performance -might- help too but if you're dealing with ghost windows or out of bounds allocations of resources it may not have anything to show.