If you press Alt+H and then select "Troubleshoot Mode...", does it still happen in that?
hey that did work! I'll just have to figure out which extension is messing things up.
actually it still doesn't work on some sites
Hmm, weird. If you create a fresh profile, is it gone then? A fresh profile will be essentially like a factory-reset Firefox, except you can go back to your previous profile to restore your data. You can find instructions here: https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems#w_6-create-a-new-firefox-profile
Try a useragent switcher and spoof a different browser. See if its the sites you visit are throttling you for using FF. Worth a test.
I'm still getting greyed out login buttons on certain sites.
So its likely not your ISP or other site issues. Looks like in another comment you said it could be an add-on. Like debugging skyrim disable all addons and enable then one at a time till you find the problem. If you do find the problem you might want to check the addons git and report a bug if not already found.
I tried that disabling addons helps with certain sites but not others. I can't find a clean fix.
Maybe try an uninstall and reinstall.
Before you uninstall in Settings -> Privacy & Security -> Cookies and Site Data, clear all site data and cookies.
That's all I got. Best of luck!
thank you sweetie 
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