Check your zoom controls.

<Control> (Mac=<Command>) + (plus) enlarge - (minus) reduce 0 (zero) restore

This probably isn't related, but since you shared your add-ons list, I'll mention that some of your extensions might have arrived as part of a bundle and might make unwanted modifications to your Firefox.

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove).

Any improvement?