I don't know if this is relevant to you, Thad, but I too am a long time user of Firefox (since its beta days).
About a couple of years ago, something they did caused some serious memory leaks and massive memory bloat (no memory cleanup even when you close different tabs). To the extent that it made FF almost unusable and I started (reluctantly) using Chrome only for this reason.
However, as of (about) 6 months ago or maybe a year ago, they have largely solved this problem and I don't see memory leaks or slow bloat even with prolonged usage.
So, if you haven't already, please do try the latest version of Firefox.
About a couple of years ago, something they did caused some serious memory leaks and massive memory bloat (no memory cleanup even when you close different tabs). To the extent that it made FF almost unusable and I started (reluctantly) using Chrome only for this reason.
However, as of (about) 6 months ago or maybe a year ago, they have largely solved this problem and I don't see memory leaks or slow bloat even with prolonged usage.
So, if you haven't already, please do try the latest version of Firefox.