First test/update: I'm now on my laptop (Macbook Air M1), running Firefox, and it's behaving entirely normally. Firefox 145.0.2, MacOS 15.7.4 (no, not 26.anything!).
Update: OK, Firefox is now at 148.0, and everything is still working normally here.
Assuming your Mac laptop isn't pretty old, you can safely update to Sequoia (15.7.4, currently). It's solid, and not too much of a space hog. I haven't updated to Tahoe (26.x) - and I won't, because neither my laptop nor my desktop (Mac Mini) has enough storage space (SSD space, not RAM) to accommodate the bloat. All that pretty UI "liquid glass" assumes I have something like 60 Gb available to update the system software - and, because I actually use these machines, I don't have that much empty space.
Update 2: Now running Chrome. All seems normal.
Update 3: Safari. Ditto.