It is not easy to tell. We have had many levels of KM 75 as shown by the data from one folder that I keep on my computer.
Prepared: 11:21 6/19/2015
Folder: C:\Users\Public\Z_Install\K-Meleon\Dorian KM75\
Include Sub-Folders? No
km75b1u1.7z 7,666,300 12/11/2014 14:49
km75b2u1.zip 1,121,478 1/26/2015 20:10
km75rc2u1.zip 1,080,861 4/2/2015 18:58
km75rc2u2.zip 1,357,735 4/9/2015 19:36
km75rc2u3.zip 1,081,864 4/14/2015 19:24
km75rc2u4.zip 1,368,020 4/15/2015 15:17
km75rc2u5.zip 1,369,115 4/18/2015 15:16
km75rc3u1.zip 1,095,545 5/9/2015 07:12
km75rc3u2.zip 1,134,014 5/14/2015 19:51
km75rc3u3.7z 2,002,665 5/19/2015 20:05
K-Meleon75 (2).7z 25,832,225 6/16/2015 16:08
K-Meleon75.0RC.exe 27,301,344 3/13/2015 15:51
K-Meleon75.7z 25,834,188 5/26/2015 19:13
K-Meleon75b1.7z 26,555,810 11/24/2014 20:14
K-Meleon75b2.7z 25,358,548 1/15/2015 14:37
K-Meleon75b3.7z 25,767,274 3/2/2015 13:17
K-Meleon75b3u1.7z 2,750,701 3/2/2015 13:12
K-Meleon75b3u2.7z 3,054,303 3/3/2015 12:57
K-Meleon75b3u3.7z 3,067,627 3/8/2015 20:20
K-Meleon75RC2.7z 25,839,282 3/30/2015 19:34
K-Meleon75RC3.7z 25,842,953 5/6/2015 09:27
Do you remember which file that you used to put KM on your computer? If not, then look in your KM root folder and find the file named "k-meleon.exe". Post back with the 'modified date' and exact file size and I will try to find a match. If I can find a match, then we will know the version.
If it is old, then it might be best to install the latest available code.
Just to test your keys again, please try this:
Press and hold the "Ctrl" key and press the "T" key. Unless you are running KM without tab support enabled, you should get a new tab.