As mentioned, use Goanna test builds. They work reliably on diverse websites and are quite stable.
You can deactivate Flash in the 'Menu' to the right so videos and anims will not load, and reactivate it on a 'per page' basis if needed.
For an elegant way to *not* load tabs while opening them, try e.g. 'UnloadTab' extension:
https://legacycollector.org/firefox-addons/345001/index.html
Set it to 'load only active tab' when starting the browser, 'do not load' new tabs, and 'unload after 1 minute' for inactive tab, will save nerves and resources when two or more pages try to play videos and stuff. Rest is up to you.
I test some addons myself right now and 'unloadtab-0.24.5' did work for me on KM 76.2 with Goanna, so I'm testing the later ones too atm.
To download do 'right click - save as...', bc .xpis will normally be installed with the KM browser.
Or use a Chromium based browser which does not care for .xpi extentions.
Do check for malware first before installing, pls use VirusTotal.com or similar, to stay safe.
In the k-Meleon 'Addons' section (type 'about:addons' in URL bar to go there) choose 'Extensions' on left and click the 'Menu' symbol on top, choose 'install addon from file', done.