Settings on your browser wouldn't effect how it shows to others on the site.
That only happens if you make the text larger within the post itself.
The settings are different in every browser, but you might want to check on setting yours to show text for this site (or any site that is to small for you) to a larger size. This way you can see it how you wish without altering it for others.
I see. And are the apps on both devices the same? No additional ones, others used, etc.? Another option would be to consider doing a "Hard Reset" of the problem tablet, which would wipe it and then restore it to its original software (prior to any use). Then you can start fresh and see if the problem continues. If it does, then it is likely not software.
However, before trying that, I have to ask, have you checked the internet/WiFi connection to see if it has any 'drops'? Some devices will run fine, ignoring any drops or slowness in access, as long as it is a short one. Where as others will go as far as to not work at all until restarted. To test that you might want to try using the problem device on a different WiFi and see if it occurs there (just to test).
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the screen.
4. Once you can see the logo, release the buttons and allow the device to enter the "System Recovery Mode".
5. Next use "Volume Down" button to get to the "wipe data/factory reset" option.
6. When in recovery mode the "Volume Up" and "Volume Down" buttons are how to can navigate and highlight what option you need.
7. Once you have selected the "wipe data/factory reset", press the "Power" button to select that option.
8. On the following screen, repeatedly press the "Volume Down" button until the "Yes - delete all user data" option is what is selected.
9. Then press the "Power" button to hard reset the tablet.
10. If you took your SD card out in step 2, when the device is up and running again, reinsert the SD card.